(Timothy A. Clary/AFP/Getty Images)

Ana Ivanovic’s promising summer, in which she returned to the WTA top 10 for the first time since 2009, came crashing to an end Thursday in the second round of the U.S. Open.

The former world No. 1 and 2008 French Open champion lost in straight sets to world No. 42 Karolina Pliskova, 7-5, 6-4, in 1 hour 20 minutes. Pliskova, a 22-year-old Czech, had never advanced past the second round of a Grand Slam.

Ivanovic, 26, entered the tournament on the heels of playing some of her best tennis in years. The Serb reached the final in Cincinnati earlier this month after beating Maria Sharapova in the semifinals. She also pushed world No. 1 Serena Williams to three sets in the quarterfinals at Stanford in July.

After winning her maiden Grand Slam title at the French Open in 2008, Ivanovic has struggled to capture her top form. She wouldn’t reach the quarterfinals of a major tournament again until the 2012 U.S. Open.

This year, she reached the quarterfinals at the Australian Open, beating Williams in the fourth round, before losing to Canada’s Eugenie Bouchard.

The second-round exit is her earliest at the U.S. Open since 2009, when she lost in the first round.

Scoreboard: ATP | WTA