In any major tennis tournament across the world, getting a direct entry to the main draw is certainly a compliment within itself. In a player-oriented sport such as tennis, only the top ranked players are given an entry to the main draw.
Depending on the level of the tournament - Grand Slams like Wimbledon, French Open, Australian Open & US Open or ATP 1000 series or lower levels, the number of players competing will vary accordingly. At any given point of time, there are numerous players looking to build their form and rise up in the rankings.
If the player is ranked at a higher position, then he/she is bound to get invited to the main draw. However, if the player is ranked lower, then they have to go through what is known as qualifiers.
The qualifiers are usually played three to four days before the main tournament.
During the qualifiers, the player has to compete with other players in the bracket who are ranked on a similar scale. The format of the qualifiers is the same as the main tournament, except the winners here gets a chance to compete in the main draw. There are no final matches played in the qualifiers. In fact, the players who make it to the final eight or four get the ticket to the main event and are marked with the ‘[Q]’ prefix.
Some of the qualifiers have gone to upset top players in the main draw and even won titles on occasions.
For instance, in the 1999 Wimbledon, Alexandra Stevenson started her run as a qualifier. After qualifying for the main draw, she moved on to reach the semifinal before losing to Lindsay Davenport. John McEnroe (1977) and Vladimir Voltchkov (2000) were the other qualifiers to make Wimbledon semi-finals.