Kristina Mladenovic's first match since her nightmarish end to the U.S. Open produced another collapse and a controversial umpire's call at the French Open on Tuesday.

The French player lost to Laura Siegemund of Germany 7-5, 6-3 after serving for the first set at 5-1.
Mladenovic was furious with chair umpire Eva Asderaki for not spotting a double bounce on set point. During a 10-stroke exchange, Mladenovic hit a drop shot that Siegemund ran for and got back over the net -- although a TV replay showed the ball bounced twice. Mladenovic slowed up, looked confused, and wound up touching the net, which automatically gave the point to Siegemund.

�Mistakes are human but I don�t see how the umpire can miss that. She didn�t see a double bounce,� Mladenovic said. �Unfortunately she will continue at Roland Garros, and I won�t continue at Roland Garros.�

For Novak Djokovic, though, his first Grand Slam action since his disqualification at the U.S. Open went as smoothly as can be.

The top-ranked Serb, who is bidding for a second title here and an 18th major title overall, beat Mikael Ymer of Sweden 6-0, 6-2, 6-3 under a closed roof at Court Philippe Chatrier. The first set lasted just 20 minutes and Djokovic broke the 80th-ranked Ymer nine times overall.

Djokovic was defaulted from his fourth-round match at the U.S. Open this month for accidentally hitting a line judge in the throat with a ball hit in anger after dropping a game.