Female Tennis Player, US Open 2011

The US Open has tiebreaks in every set, including the last set. The other three Grand Slam tournaments have tiebreaks in every set other than the last set (i.e. the fifth set for men and third set for women), and therefore their last set continues indefinitely until a two-game lead is reached.
History
The US Open has grown from an exclusive entertainment event for high society to a championship for more than 600 male and female professional players who, as of 2008, compete for total prize money of over US$21 million, with $1.5 million for each winner of the singles tournaments.