Key Biscayne, Fla. (AP)—Maria Sharapova was happy to play an 11 a.m. match Monday, especially when her work day was already done by the time a mid-afternoon shower interrupted play.

''It's nice to see all the players coming back in the locker room, and I'm like, 'I'll see you later,''' she said.

Sharapova started early but didn't start well. She won only five points in the first four games before settling down to reach the quarterfinals at the Sony Open by beating Kirsten Flipkens 3-6, 6-4, 6-1.

The world's top-ranked players had an easier time. Serena Williams eliminated fellow American CoCo Vandeweghe 6-3, 6-1. Rafael Nadal received a warning for slow play and still won in 59 minutes against Denis Istomin, 6-1, 6-0.

No. 10 seed John Isner, the only American to reach the men's third round, hit 17 aces and beat Nicolas Almagro 7-5, 6-3.

The lack of upsets so far means players with a total of 66 Grand Slam titles will be in action Tuesday, including Sharapova, Williams, Nadal, Roger Federer and Novak Djokovic.

More than the other top contenders, Sharapova has flirted with an early exit. She endured her second successive ragged three-setter and found herself trailing Flipkens 4-0 after only 15 minutes.

''I usually like playing the first match, but I didn't start off the way I wanted to,'' she said. ''Nothing was working.''

Seeded No. 4, Sharapova seemed thrown off by the lack of pace from Flipkens, a tour veteran who hits floating backhands and sometimes slices her forehand as well.

''She's a different type of opponent,'' Sharapova said. ''There are not too many girls that hit a slice backhand 90 percent of the time in the rallies. But I know what to expect from her game. It shouldn't be that much of a surprise.''

Sharapova finished with 36 unforced errors and only 13 winners. She also double-faulted 10 times.

But she won — and was ready to leave Crandon Park before most matches had even begun. With the rest of the day free, what was on the schedule for one of the world's most celebrated athletes?

''Not much, actually,'' Sharapova said. ''I like to have my afternoon tea around 5. It's like a Russian tradition. I'll see my dog, spend some time with him, then get treatment, dinner, and then the day is over.''

At the top of her to-do list for the rest of the week is winning her first Key Biscayne title. Sharapova has been the runner-up five times, including each of the past three years, but she downplays any frustration regarding her many near-misses.

''Of course you want to be able to hold the winner's trophy,'' she said. ''But you also remember the matches that you got through to get in the position to get to the final stage. It's not like I didn't have my opportunities in those finals; I just didn't take them. That's why you come back and hope for another chance.''

Williams seems to be gaining momentum as the tournament unfolds, as usual. She overcame sloppy patches in her first two matches and committed only one unforced error in the second set against Vandeweghe.

But Williams was impressed with the 22-year-old American, and told her so when they met at the net after the match.

''She said, 'Listen, you played so well. We've got to play doubles. We'd do so well,''' Vandeweghe said.

Williams' opponent Tuesday night will be No. 5-seeded Angelique Kerber, who beat Ekaterina Makarova 6-4, 1-6, 6-3. No. 8 Petra Kvitova rallied past No. 12 Ana Ivanovic, who double-faulted nine times in the final two sets and lost 3-6, 6-0, 6-0.

In other men's third-round play, No. 22-seeded Alexandr Dolgopolov rallied from a break down in the final set to beat Dusan Lajovic 3-6, 6-0, 7-6 (5). Dolgopolov has gone 6-1 this month despite his worries about unrest in his native Ukraine, where his mother and other relatives still live.

''For me it was important it has calmed down and no people are dying,'' said Dolgopolov, who was born in Kiev. ''But there's a little bit of chaos still going on, and no one knows who is the ruling party and who is controlling the country. It's a mess.''