By Shrivathsa Sridhar PARIS, May 31 (Reuters) - Iga Swiatek's 25th birthday celebrations turned sour at the French Open on Sunday, as the former champion lost to 15th seed Marta Kostyuk in the fourth round and her bid for a fifth title ended just when she had looked to be rediscovering her form.

The Ukrainian ousts the Polish four-time French Open champion in straight sets, enters first quarters at Roland Garros

Kostyuk's work to separate her self-worth from her results has led to the flourishing of a player whose talent was never in doubt.

PARIS, May 31 (Reuters) - Marta Kostyuk's love affair with clay has blossomed into a full-blown romance after the Ukrainian stunned world number one Iga Swiatek 7-5 6-1 to reach her first Roland Garros quarter-final on Sunday.

For years, Kostyuk has been one of the most vocal sportswomen when it comes to condemning the Russian invasion of Ukraine.