The 23-year-old Serbian has already reached two semi-finals in Grand Slams this year (French Open and Australian Open) but has never made it to a final in 20 career major appearances.

This is the sixth straight US Open for second seeded Jankovic who moves through to the second round where she will face Swede Sofia Arvidsson who beat China's Yan Zi 6-2, 6-4.

Jankovic has six career singles titles but just one victory this year despite reaching the quarter-finals in 14 of 15 tournaments she has played.

Jankovic needed just 27 minutes to win the second set on Monday, forcing the 16-year-old Vandeweghe into making mistakes especially when the American attacked the net.

"It is tough to play opponent who doesn't have anything to lose," Jankovic said. "I didn't know anything about her going into the match. I didn't know she was 16 until they made the announcement before the match. I did as much as I needed to win the match."

Vandeweghe finished with a total of 33 unforced errors to Jankovic's 13. Jankovic won 80 percent of her first serve points and coverted four of eight break point opportunities in the 60 minute match at the Arthur Ashe Stadium.

Jankovic comes to New York with one main question hanging over her head -- as the competition improves in a Grand Slam can she raise her level of play sufficient enough to get into a final.

"Of course, I want to keep improving," she said. "The priority is to be healthy and I haven't been healthy throughout the year.

"I pray to God to stay way I am now."

She surpassed countrywoman Ana Ivanovic earlier this month to become the world's top ranked female singles player but held the distinction only briefly before dropping back to No. 2.