Updated September 11, 2026
Frances Tiafoe and Ben Shelton meet Friday, September 11, in an all-American US Open semifinal after both survived exhausting five-set quarterfinals. Shelton enters as the clear favorite after knocking out defending champion Carlos Alcaraz, while Tiafoe produced his own remarkable escape from two sets down against Alex Michelsen. Polymarket currently gives Shelton roughly a 73% chance to reach the final and Tiafoe about 27%, but the total-games market is where my projection sees a meaningful gap in the prediction markets.
Why Our Model Sees Value:
“Shelton deserves to be favored to advance, but his advantage in match-winner pricing does not necessarily translate into a short semifinal. Tiafoe has already shown that he can extend Shelton over five sets at this tournament, while both players have enough serving power and hard-court offense to create sets decided by a single break or a tiebreak. The market appears to be placing too much weight on Shelton's superior overall level and not enough on the game-count implications of the styles of these players.”
At Least 4 Sets Expected
Polymarket has Over 40.5 Games near 49%, while its related markets price Over 3.5 Sets at 62% and Over 4.5 Sets at 29%. The match does not need to reach a fifth set for the 40.5-game total to clear. Four reasonably competitive sets can be enough, particularly if one reaches a tiebreak.
A Higher Projected Total
My projection puts the total around 42 to 43 games on average and gives Over 40.5 a 53.5% chance. The gap is not enormous, so this is a price-sensitive prediction rather than one to chase significantly above the current price. At 49¢, though, our projection has a 4.5% edge. I would still consider it playable through roughly 51¢.
Recommended Prediction:
Over 40.5 Games
Current Market Price:
49¢
Model Win Probability:
53.5%
Market-Implied Probability:
49%
Model Edge:
4.5%
Buy Up To:
51¢
Model Trade Confidence:
74/100
Shelton owns a 3-1 career advantage over Tiafoe, but their history is more competitive than that record looks. Their 2 previous US Open meetings have produced very different outcomes. Shelton won their 2023 quarterfinal in 4 sets, 6-2, 3-6, 7-6, 6-2, before Tiafoe answered in 2024 with a 5-set victory, 4-6, 7-5, 6-7, 6-4, 6-3. Shelton then won their most recent meeting in Washington in 2025, 7-6, 6-4.
That history is useful for those making a Tiafoe vs Shelton prediction on the total because Tiafoe has already demonstrated that Shelton's serve does not automatically push him out of matches on this surface. Their 2024 US Open meeting reached 54 games, and their 2023 meeting included a tiebreak and 4 sets. Shelton has been the more successful player overall, but Tiafoe's style can force him to play additional balls and defend his second serve more than usual.
Shelton's win over Alcaraz was arguably the best major victory of his career. He recovered after losing the opening-set tiebreak to win 6-7, 6-1, 6-3, 1-6, 7-6, finishing the match with a 146 mph ace at 3:33 a.m. The contest lasted 4 hours, 28 minutes and marked Shelton's first victory over a Top 3 opponent after 17 previous losses.
The serving numbers explain why Shelton is such a difficult matchup in New York. Against Alcaraz, he generated 54 unreturned serves and reached 149 mph, allowing him to shorten points even as the match stretched deep into a fifth set. He also handled short rallies well and finished with fewer unforced errors than Alcaraz.
That serve is a major reason Shelton is priced as the favorite. It is also one reason the Over remains interesting. When Shelton is serving efficiently, sets can stay on serve for long stretches. A 7-6 set contributes 13 games without requiring either player to dominate.
Tiafoe's quarterfinal was no easier. He trailed Michelsen by 2 sets and a break before recovering for a 5-7, 3-6, 7-5, 6-3, 7-6 victory. Michelsen even served for the match in the third set before Tiafoe broke back and gradually raised his level.
The late stages of that match were especially encouraging for this prediction. Tiafoe struck 7 aces in the fifth set after producing just 3 across the opening 4 sets. He also improved to 6-1 in deciding-set tiebreaks during 2026. Those numbers suggest a player who remains dangerous late rather than one whose serve fades automatically as matches grow longer.
Both players arrive after roughly 4.5-hour quarterfinals. Tiafoe's match lasted 4 hours, 38 minutes, while Shelton's ended at a record 3:33 a.m. Shelton therefore had an unusual recovery schedule after the biggest win of his career. His team immediately focused on hydration, food, light cycling, stretching, and sleep management before the semifinal.
Fatigue is the strongest argument against the Over. If either player struggles physically, the semifinal could become one-sided quickly. Still, they have had additional recovery time before Friday, and both have repeatedly shown the ability to maintain serving quality deep into long matches.
Shelton is the stronger candidate to reach the final. His first serve gives him the easiest route to cheap points, and his performance against Alcaraz represented a higher level than anything Tiafoe has produced during this tournament. Polymarket's roughly 73% price on Shelton to advance reflects that difference.
The total does not require Tiafoe to win, however. A Shelton victory such as 7-6, 6-4, 4-6, 6-4 would already produce 43 games. Tiafoe taking one set, combined with one especially tight Shelton set, puts Over 40.5 in a strong position.
That is where my projection separates from the market. Shelton can be the better player and still need considerable time to finish this match. Given their US Open history, Tiafoe's current level, Shelton's reliance on serve-heavy sets, and the possibility of at least one tiebreak, Over 40.5 Games is my preferred position.