Every esports fan has seen it: a top team loses to a much weaker side in a group stage, and social media declares the favourites finished. Then the same top team cruises through the playoffs. Often the explanation is simple. The upset happened in a best-of-one.
Series length is one of the most underrated factors in esports results. Here's why it matters so much.
The maths of upsets
Imagine a strong team that beats a weaker one 70% of the time on any single map. In a best-of-one, the weaker team wins 30% of the time. That's almost one match in three.
In a best-of-three, the weaker team has to win two maps before the stronger team does. The chance of that drops to about 22%. In a best-of-five, it falls further, to roughly 16%.
Longer series don't remove upsets. They make them rarer, and they make an upset more likely to mean something. A team that wins a best-of-five against a favourite usually earned it. A team that wins a best-of-one may just have had a great half.
Map pools and preparation
In CS2 and Valorant, series length also changes which maps get played.
In a best-of-one, teams ban maps until one is left. Both sides avoid the opponent's best maps, so the match often lands on a map neither team loves. A team with one exceptional map and nothing else can do well in best-of-ones, as long as that map keeps coming up.
In a best-of-three, each team picks a map. Now you need at least two strong maps, and you'll have to play the opponent's pick too. A third, decider map tests depth even further.
In a best-of-five, a team needs a real map pool. Weaknesses that a best-of-one can hide get exposed.
League of Legends has a similar effect through Fearless Draft. In a best-of-five, champions can't be repeated, so a team's whole champion pool is tested over the series. We explain how that works in Fearless Draft explained.
Adapting mid-series
Longer series also reward teams that can adjust. After a lost map, a team can change its approach, target a weak player, or switch to a strategy it saved. Some teams are famous for losing the first map and then taking the series once they've read the opponent.
In a best-of-one, there's no time for that. Whoever prepared better for that single map, or simply started better, usually wins.
Fatigue and pressure
Best-of-fives can run four or five hours. Focus drops, and the players who stay calm in the fourth or fifth game often decide the result. Experienced teams tend to do better here, which is one reason the same organisations keep winning big finals.
Why organisers still use best-of-ones
If best-of-threes are fairer, why use best-of-ones at all? Time. A tournament with 16 or 32 teams can't fit best-of-threes for every match into a few days. Many events compromise: best-of-one early in a group or Swiss stage, and best-of-three when a team's place is on the line. Our Swiss format explainer covers how that mix works at Majors and Worlds.
There's also a case for best-of-ones as entertainment. They're short, unpredictable, and every round matters. Some fans love that.
How to read results with this in mind
- Check the format before reacting. A best-of-one loss is a warning sign, not a verdict.
- Look at map scores, not just series scores. A 2–1 where the loser won its own pick convincingly says something different from a 2–1 decided in overtime on the last map.
- Weight playoff results more. Rankings systems, like CS2's Valve Regional Standings, give more weight to strong results at big events, partly for this reason.
- Notice map pool patterns. A team that only wins on its own picks may struggle when it meets a team with a deeper pool.
The next time a favourite drops a best-of-one, remember the 30%. It happens more often than it feels like it should.
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