Ask a casual fan why Grand Slam tennis feels different from a regular tour stop, and most will point to the crowds, the history, the two weeks of buildup. Ask a bettor the same question, and they’ll point somewhere more specific: the scoreboard. Best-of-five sets doesn’t just make matches longer — it fundamentally changes how likely the favourite is to actually win. And nowhere is that more visible than in the swings you’ll see on the Wimbledon betting odds board. As soon as the men’s draw shifts into its longer format for the fortnight, the prices go berzerk. 

The Math Behind It

The math behind this is refreshingly simple. Every set is essentially a mini-experiment in who’s better on the day, and stacking more experiments together smooths out the noise — a lucky net cord, a rain delay, a hot service game that swings a short match but gets diluted over a longer one. Modelling from betting analysts shows just how much this matters in practice. 

Take a player projected to win any given set 60% of the time: over a best-of-three match, that translates to a 64.8% chance of winning the match. Stretch the same player out to best-of-five, and their win probability climbs to 68.3% — a meaningful jump of roughly 3.5 percentage points. Push the set-win probability up to 70%, and the gap between formats widens even further, to over 5 points. The pattern holds across the data: the closer the matchup, the bigger the format effect, which is exactly the zone where bettors spend most of their time looking for value.

Tour-level results back this up. Looking at matches between 2010 and 2024, roughly 29% of best-of-three matches on the regular ATP tour ended in a genuine upset — a lower-ranked player beating a clear favourite. At the Grand Slams, where the men’s draw is played best-of-five, that upset rate drops to around 24% once you control for ranking gap and surface. That’s a real, consistent edge for the favourite, and it lines up almost exactly with what the theoretical models predict.

How to Make Use of This Knowledge

What does this mean if you’re trying to read a draw? A few practical takeaways. First, underdogs are live in shorter formats in a way they simply aren’t over five sets — qualifiers, big hitters, and streaky young players tend to have more bite when a bad set or two can’t be absorbed by a third comeback opportunity. Second, physical conditioning and five-set history become far more relevant metrics once a match can stretch past three hours, which is why so much pre-tournament coverage at majors obsesses over a player’s fitness and past deep-match performances. And third, in-play momentum swings harder in best-of-three: a single early break matters more when there are fewer sets left to erase it.

It’s also worth remembering how rare the best-of-five format actually is. Outside the four majors and the odd Davis Cup tie, virtually the entire tour — ATP 250s, 500s, Masters 1000 finals, the ATP Finals — is played best-of-three. That’s not a coincidence; shorter matches are more sustainable for players’ bodies over a long season and easier for tournaments to schedule around weather delays.

So the next time a lower-ranked player is given a puncher’s chance against a seed, check the format before you check the ranking gap. Three sets and five sets aren’t just different lengths of the same contest — they’re different tests entirely, and the numbers back that up. For a deeper look at how playing surface adds another layer to that equation, our ATP and WTA betting guide for beginners breaks down how court speed interacts with match length to shape a tournament’s outcomes.