tetlock-style-economists - Predictions for:

The event is already definitively resolved as No. Iga Świątek was eliminated by Qinwen Zheng in the round of 16 on September 7, 2026, losing 5–7, 3–6. Since reaching the semifinals required advancing through the quarterfinal stage, her elimination made the event impossible. The later September 30 resolution date does not change the completed outcome, so the probability that the event occurs is 0%.

I estimate a 40% probability that Iga Świątek reaches the 2026 US Open semifinals. The key clarification is that she has already reached the round of 16, so the event now requires two wins: against Qinwen Zheng and then against either Elena Rybakina or Naomi Osaka.

As a historical base rate, a top-tier but non-top-four seed reaching the semifinals from the round of 16 is often in the roughly 30%–45% range, depending on the draw and opponent quality. Świątek’s strong US Open record and current form place her toward the upper part of that range, but her likely quarterfinal opponent is unusually difficult.

Factor estimates:

• Win over Zheng: approximately 78%. Świątek has a 7–1 record against Zheng, is in strong recent form, and has won all three matches without dropping a set. Zheng’s momentum, power, and four consecutive three-set victories prevent this from being closer to 85% or higher.
• Quarterfinal opponent: Rybakina is the more likely opponent, probably around 65%–75%, with Osaka accounting for most of the remainder. Rybakina has been excellent through three rounds and presents a particularly difficult matchup, while Osaka’s leg issue adds uncertainty.
• Win in the quarterfinal: approximately 48% if facing Rybakina and approximately 60% if facing Osaka, assuming Osaka is reasonably healthy. This gives a weighted quarterfinal-win probability near 51%–53%.

Combining the stages gives approximately 0.78 × 0.52 = 0.41, which I round down slightly to 40% to account for uncertainty around Świątek’s physical recovery after the demanding Bouzková match and the possibility that Zheng extends the match substantially.

The positive case is supported by Świątek’s 13–1 recent record, her Toronto win over Rybakina, six straight US Open fourth-round appearances, and her ability to win pressure tiebreaks. The negative case is her uneven broader 2026 season, the close nature of the Bouzková match, Zheng’s momentum, and the likelihood of facing a healthy Rybakina.

I would therefore use 40% as the central estimate, with a reasonable uncertainty range of approximately 36%–44%. A routine win over Zheng combined with an Osaka victory over Rybakina would move the probability higher; a long Zheng match followed by a strong Rybakina performance would lower it.

I estimate a 40% probability that Świątek reaches the 2026 US Open semifinals. The event is already at the third-round stage, so she needs only three more victories, but the projected route remains difficult.

Base rate: A No. 8 seed and former US Open champion would ordinarily have a meaningful but clearly below-even chance of reaching the semifinals, perhaps around 30–40% at this stage depending on the draw. Her recent US Open record is encouraging—she has reached at least the quarterfinals in each of the last three editions—but she has not progressed beyond the quarterfinal since winning in 2022.

Factor 1, defeating Marie Bouzková: Świątek is a strong favorite based on her recent straight-set win over Bouzková, superior offensive weight, and excellent opening-round form. I assign roughly an 85% chance.

Factor 2, winning the round of 16: The likely opponents include Osaka, Mertens, Keys, or Zheng. This is substantially more difficult than the first two rounds, particularly against Osaka, Keys, or Zheng, who can take time away from Świątek on hard courts. I assign roughly a 72–75% chance, using 74% as a midpoint.

Factor 3, winning the quarterfinal: A healthy Rybakina is a highly challenging opponent, although Świątek defeated her decisively in Toronto and Rybakina recently retired in Cincinnati. Accounting for the possibility that Rybakina is eliminated or not fully fit, I estimate Świątek's quarterfinal win probability at approximately 52–55%.

Using representative figures of 0.85 × 0.74 × 0.54 gives approximately 34%. I raise the overall estimate modestly to about 40% because the quarterfinal opponent is not certain, Świątek's Toronto title and two efficient wins are strong positive evidence, and the simple multiplication approach can understate the benefit of favorable draw developments such as Rybakina's early exit. Conversely, the estimate is held below 50% because her 2026 season has been inconsistent, the quarter is unusually strong, and her recent US Open ceiling has been the quarterfinal.

The main reasons this forecast could be wrong are an unexpectedly strong performance from Rybakina, Osaka, Keys, or Zheng; an injury or long match for Świątek before the quarterfinal; or, in the opposite direction, another routine win combined with Rybakina's physical problems. Given the research and the prior estimates of 42% and 43%, 40% is a calibrated central estimate rather than a strong directional change.

1. Clarification: The event is that Świątek wins enough matches to reach the 2026 US Open singles semifinals. Given that she has already won her first-round match, this is now a conditional forecast from the second round onward, rather than a pre-tournament estimate.

2. Historical base rate: For an elite top-eight WTA player, reaching the US Open semifinals typically has a rough unconditional probability in the 25–40% range, depending on draw and form. Świątek’s own history is mixed but strong: she won the 2022 event and reached the quarterfinals in 2024 and 2025. Those recent quarterfinal exits suggest that reaching the last four is plausible but not automatic.

3. Relevant factors:

• Current form: Strongly positive. A Toronto WTA 1000 title, a Cincinnati semifinal, and a dominant first-round win indicate good hard-court level. This raises her estimate above a neutral historical baseline.
• Early-round position: Also positive. As the No. 8 seed, she should avoid most top players until the later rounds, and the first-round win was efficient, with no break points faced. However, an expected first-round victory provides only a modest update.
• Coaching and preparation: The addition of Francisco Roig and her decision to skip mixed doubles are modest positives, suggesting improved tactical focus and energy management, though these are difficult to quantify.
• Main risks: She still needs to win three further matches, including a likely difficult quarterfinal. Players such as Pegula, Rybakina, or another top opponent could make that match close. Fatigue, a poor matchup, or a bad serving day could end the run.

4. Rough decomposition: I estimate approximately 90–95% to win the second round, 75–85% to win the third round, 65–75% to win the round of 16, and 55–65% to win a likely quarterfinal against a strong opponent. Multiplying representative values gives an overall probability around 35–45%, with the current form supporting the upper part of that range.

5. Overall forecast: 43%. This is slightly above the previous 42% estimate because the tournament-opening performance and pre-US Open hard-court results confirm favorable current form. The increase is deliberately small because the first-round win was expected and the decisive quarterfinal hurdle remains ahead.

6. Why this could be wrong: The provided dossier may overstate the value of recent results, the draw may be substantially tougher than anticipated, or her recent deep North American runs may create fatigue. Conversely, a favorable draw or continued dominant serving could make the true probability closer to 50% or higher.

I estimate a 42% probability that Iga Swiatek reaches the 2026 US Open semifinals.

Historical base rate: For an elite top-10 player at a Grand Slam, reaching the semifinals is usually a roughly 25–40% outcome, depending heavily on draw and surface. Swiatek’s US Open record is stronger than average: she won in 2022 and reached the quarterfinals in 2024 and 2025, though she has not consistently converted those quarterfinal appearances into semifinals.

Positive factors include her recent hard-court form. Winning Toronto and reaching the Cincinnati semifinals indicate good preparation and match rhythm, while her reported first-round victory confirms that she has avoided an immediate upset. Her ranking and seeding should also provide a relatively favorable path through the early rounds, and she has proven Grand Slam-level ability and prior success in New York.

The principal negative factor is the quarterfinal hurdle. At that stage she is likely to face another top player, and the dossier specifically identifies Jessica Pegula as a difficult matchup after a recent Cincinnati loss. A No. 8 ranking also means she is less likely than a top-four seed to receive a structurally easy quarterfinal path. Hard courts offer Swiatek fewer margins than clay, and a single poor serving or return performance can end the run.

A rough decomposition is: about 75–80% to reach the quarterfinals given her form and seeding, multiplied by approximately 50–55% to win a likely quarterfinal against a strong opponent. This produces an overall estimate near 40–44%. I use 42% as the central estimate. The main uncertainty is the draw: a favorable quarter could raise the probability above 50%, while a difficult quarter containing another elite hard-court player could reduce it toward 30–35%.