This was Ivanovic's first match since her injury withdrawal at Wimbledon
Former world number one Ana Ivanovic made hard work of her second-round win over Vania King at the LA Women's Tennis Championships in Los Angeles.
The sixth-seeded Serb suffered a mid-match slump but rallied to beat American wildcard King 6-4 4-6 6-1.
She will face either 13th seed Samatha Stosur of Australia or Maria Kirilenko of Russia in the third round.
Russian second seed Vera Zvonareva also struggled before overcoming China's Shuai Peng 3-6 6-3 7-6 (8-6).
Chinese duo Zheng Jie, seeded 14th, and Li Na, seeded 12th, made up for compatriot Peng's brave defeat by sealing their places in the third round.
Zheng defeated Ukraine qualifier Olga Savchuk 7-5 1-6 6-2 while Li advanced when Japan's Ayumi Morita retired after losing the first eight games of their first-round match.
It's just the first match and I have the ability to improve. I had an opportunity a few times to put the ball away but had a little doubt in my mind as to which shot to take.
Stosur, who beat Serena Williams on her way to the semi-finals of the WTA Bank of the West Classic title in California last week and is seeded 13th in LA, made light work of Romanian Monica Niculescu, beating her 6-1 6-2.
Seeking her first title since October 2008, Ivanovic struggled with King's relentless counterpunching in the first two sets but in the final set, last year's French Open champion was able to overpower her plucky opponent.
"I felt happy with the way I was moving and playing," said Ivanovic, on court for the first time since a thigh injury forced her to retire from a Wimbledon fourth-round match against Venus Williams in late June.
"It's just the first match and I have the ability to improve. I had an opportunity a few times to put the ball away but had a little doubt in my mind as to which shot to take."
Second seed Zvonareva, who received a bye in the first round, lost the first set to world number 38 Peng and looked in danger of falling victim to a surprise exit but rallied to claim victory in two hours, 19 minutes.
She now faces either American Jill Craybas or Belgian Yanina Wickmayer, who play on Wednesday, in round three.