Five-set Grand Slam tennis is a different proposition to the standard ATP three-set matches, but how does it affect a player's chance of winning, and therefore your betting strategy? This tennis Grand Slam trading strategy gives tennis bettors an insight into why Grand Slam matches can make the favourite 5% more likely to prevail compared to best-of-three sets.

## Calculating the effect of five-set Grand Slam events

The best way to identify the effect of longer best-of-five set matches compared to the traditional best-of-three is to calculate a win percentage for each player.

As an example, let’s say Player A has a 70% chance of winning each set against Player B. The probability of winning each set (W) is therefore 0.7 for Player A and the odds of him not winning the set are 0.3 (L).

There are three possibilities of Player A winning a three-set game:

- (W*W) = Player wins the first two sets.
- (W*L*W) = Player wins the first and third set, while losing the second.
- (L*W*W) = Player loses the first and wins the next two sets.

To calculate a player's chance of winning a three-set match use the following formula:

Player's chance of winning = (W*W) + (W*L*W) + (L*W*W)

For our example where Player A has a 70% chance of winning each set, his chances for winning the match are:

If the two same players played in a best-of-five Grand Slam match, do Player A’s chances of winning the game improve?

Given the potential extra sets in a five-set match, the calculation is different.

There are three possibilities of Player A winning a five-set match (3-0, 3-1 or 3-2), and each can happen in a different sequence:

- 3-0 = (W*W*W) (one possible sequence)
- 3-1 = (W*L*W*W), (L*W*W*W) and (W*W*L*W) (three possible sequences)
- 3-2 = (W*W*L*L*W), (W*L*W*L*W), (W*L*L*W*W), (L*L*W*W*W), (L*W*W*L*W), (L*W*L*W*W) (six possible sequences)

To calculate a player's chance of winning a five-set Grand Slam match use the following formula:

Player's chance of winning = (W*W*W) + (W*W*W*L)*3 + (W*W*W*L*L)*6

Therefore, the chances of Player A winning a best-of-five Grand Slam can be calculated as:

The difference in win ratio for Player A increases to 5.3% simply by playing Player B in a five-set match compared to a three-set match.

The following graph shows how the probability of a favourite winning a match increases up to a point, depending on the perceived differences in ability, when playing a five-set match compared to a three-set match.

This example details the basic difference between playing a five-set Grand Slam tournament compared to a three-set ATP Tour event and how this helps a favourite’s chances of winning.

The impact will increase or decrease depending on the differences between the two players' perceived ability; the greater the disparity in ability, the bigger the advantage for the favourite - up to a certain point (72.35%) - over five sets.

Essentially, the more sets you need to win a match, the lower the chance variance has on impacting the result. For instance if Player A played Player B in 1000 five-set matches, the better player would most likely win according to the law of large numbers, as the favourite’s win ratio would convey to its theoretical probability.

## How often do pre-game tennis favourites win in Grand Slams?

From the calculations above, we know that a better player’s chances of winning a match improve (in our example by 5.3%) by playing five sets compared to three.

Now, let’s look at all Grand Slam (five-set) data from 2007-2016 to see how often match favourites win compared to ATP 250, 500 and 1000 (all three-set) data from 2010-2016. Data was only collected for all completed matches, and odds were recorded just before the off.

In the 4,838 Grand Slam matches recorded, pre-game favourites won 78.5% of the time (increasing to 78.9 in the last seven years), which as the graph above shows was consistently higher, compared to other ATP tournament types.

Favourites in three-set 250 events won on average 68.5%, while this figure rises slightly for the more important 500 (70.5%) and Masters 1000 events (70.8%).

## Apply this to betting

The data above shows that by expanding the match format to five sets from three sets increases the favourite’s chances of winning the match, as randomness (variance) reduces due to the longer format.

Tennis bettors should be aware of the different conditions that are presented from the five-set format of Grand Slams, compared to the normal three-set ATP format, and treat each independently for any tennis betting strategy.

The next step is to delve into the data to see if a favourite’s win percentage is affected by situational factors such as the differences in surface, and player motivation.