Ivanovic has won 48 matches this year, more than anyone else on tour. (Source: AP)

Ana Ivanovic kept her hot streak rolling with a straight-set victory to start the U.S. Open.

The eighth-seeded Serb beat American Alison Riske 6-3, 6-0 in the first round Tuesday. Ivanovic has won 48 matches this year, more than anyone else on tour.

The 2008 French Open champion has struggled to get back to that level but finally seems to be inching closer. She returned to the top 10 this month for the first time in more than five years.

“The confidence is on a high level,” she said. “I had a great season behind me.”

The 24-year-old Riske made a breakthrough at last year’s U.S. Open, reaching the fourth round after an upset of Petra Kvitova. She reached a career-high ranking of No. 40 this summer.

Ivanovic was broken in the first game Tuesday but quickly took control. She’s won three tournaments this year, tied with Maria Sharapova for second behind Serena Williams.

Ivanovic upset Williams to reach the Australian Open quarterfinals. She was playing well heading to Roland Garros but lost in the third round to Lucie Safarova.

In her last tuneup before coming to New York, Ivanovic beat Sharapova in the semifinals in Cincinnati before losing to Williams in the title match.

Samantha Stosur, the 2011 U.S. Open champ, also quickly dispatched a young American, beating Lauren Davis 6-1, 6-4. The 49th-ranked Davis fell to 0-3 at her home Grand Slam event.

On the men’s side, American Sam Querrey improved to 3-9 in five-set matches with a 6-2, 4-6, 6-4, 4-6, 6-3 win over Argentina’s Maximo Gonzalez.

Tenth-seeded Kei Nishikori of Japan cruised to a 6-2, 6-4, 6-2 victory over American Wayne Odesnik, showing no apparent effects from a toe injury that hampered his preparations. The 176th-ranked Odesnik earned a wild card into the U.S. Open, his first appearance in five years. He served a yearlong ban after pleading guilty for importing human growth hormone into Australia.

2004 champ Kuznetsova loses

Svetlana Kuznetsova lost her first-round match at the U.S. Open for the first time since 2005, the year she was the tournament’s defending champion.

Kuznetsova, seeded 20th this time, was beaten 3-6, 6-2, 7-6 (3) on Tuesday by 82nd-ranked Marina Erakovic of New Zealand.

“It’s disappointing, it’s shocking, to lose (in the) first round,” said Kuznetsova, who won a hard-court tuneup tournament in Washington this month.

“I was not moving my feet, was not doing anything. And then, of course, she (started) to believe,” Kuznetsova said. “In the end, it was just horrible.”

The 29-year-old Russian is a two-time major champion: She won titles at Flushing Meadows in 2004 and at the French Open in 2009.

Erakovic, meanwhile, has never been past the third round at a Grand Slam event and was 0-4 at the U.S. Open until Tuesday.

Kuznetsova was asked whether this year’s tournament was special to her, because it is the 10th anniversary of her title in New York.

“I didn’t care,” she replied. “It’s one more U.S. Open.”