Former US Open champion Sam Stosur of Australia and fellow seed Sloane Stephens were both knocked out on the opening day of action at Wimbledon.
But two-time semi-finalist Victoria Azarenka won for the first time since returning from three months out.
There was an opening-day victory for five-time champion Venus Williams, who is now seeded 30th.
Another former winner, Petra Kvitova of the Czech Republic, and second seed Li Na of China also advanced.
Kvitova, the 2011 winner, defeated compatriot Andrea Hlavackova 6-3 6-0 while Li, the 32-year-old Australian Open champion, who has reached the quarter-finals three times, beat Polish qualifier Paula Kania 7-5 6-2.
The 17th seed Stosur fell 6-3 6-4 to unseeded Belgian Yanina Wickmayer, while Stephens, the 18th seed, was beaten 6-2 7-6 (8-6) by Russian Maria Kirilenko.
Stosur's defeat continued her miserable record at the tournament, with the Australian never getting past the third round. She has lost in the opening round on six of her 12 appearances.
Stephens was way short of her best in her loss to Kirilenko, a former top-10 ranked player who reached the 2012 quarter-final, but is now ranked 87th after a knee injury.
The 21-year-old American had to save five match points in the 12th game of the second set, and had two set points in the tie-break, but Kirilenko held her nerve to secure a second-round meeting with China's Peng Shuai, who beat Britain's Johanna Konta in three sets.
Azarenka, the eighth seed, who has missed much of the season with a foot injury, overcame 1999 semi-finalist Mirjana Lucic-Baroni 6-3 7-5.
Azarenka looked strong in the first set but the 32-year-old Lucic-Baroni rolled back the years in the second set and asked more questions of the Belarusian.
She had set points on both her own serve and the Azarenka serve but was unable to convert and the 24-year-old sealed the win when a Lucic-Baroni forehand went long.
"I am so happy to get the win," she told BBC Sport afterwards, having lost to Italian Camila Giorgi on her return to action at Eastbourne last week.
"It was important to stay in the second set because it was tricky and my game was a bit up and down.
"I'm really happy to stay in and fight for every point and try to improve for the next match."
Williams recovered from losing the second set against Spain's Maria-Teresa Torro-Flor to win 6-4 4-6 6-2, thanks to 11 aces and 41 winners.
It was her first win at the tournament since 2011 after she lost in the first round in 2012 and missed last year's event because of a back injury
Five-time champion Venus Williams won her first singles match at Wimbledon since 2011 with a 6-4, 4-6, 6-2 victory over Maria-Teresa Torro-Flor of Spain.
The 22nd seed Ekaterina Makarova from Russia also went through after defeating 43-year-old Kimiko Date-Krumm of Japan 3-6 6-4 7-5.