There were upsets Sunday, including Yaroslava Shvedova's 62 64 surprise over Caroline Wozniacki.
Yulia Putintseva carried her momentum from the qualifying into her match with Serena Williams.
Williams was down 3-1 early on but took the first set in a tie-break, then went on to win, 76(5) 61.
Williams scored her 26th match win of the year, tying Sara Errani for most match wins of anyone.
Li Na wasn't as lucky, though, falling to last minute lucky loser Madison Keys in a stunner, 63 62.
Petra Kvitova was 4-2 down in the third but escaped an upset, beating Yanina Wickmayer, 46 75 64.
Agnieszka Radwanska came from 3-1 down in the second set to beat Tsvetana Pironkova in two, 62 64.
Radwanska has been turning heads at the Mutua Madrid Open this week with her shiny new blonde locks.
Radwanska was on the practice courts for a coaching clinic with some local players from Madrid.
Radwanska is a very solid No.4 - she has an almost-1000 point cushion ahead of the World No.5, Li.
Radwanska, a 12-time WTA champion, posed for photos with the players from the coaching clinic.
Meanwhile, the World No.3 - Victoria Azarenka - had a crowd assembled as she hit the practice court.
And same goes for World No.2 Maria Sharapova, who touched up her game on the practice courts, too.
Samantha Stosur, the World No.9, took some time out to visit the Samsung stand on the grounds.
After trying her hand at a cycling game, Stosur then met fans and posed for photos with them.
Stosur is always one of the biggest threats on clay - she was the French Open runner-up in 2010.
Also on Sunday, a moment of silence for the late ATP Executive Chairman and President Brad Drewett.
Dozens of ATP World Tour and WTA players, coaches and staff assembled on center court for it.
The 'Big Four' from the ATP World Tour and the WTA's World No.1, Serena Williams, at the moment.
Drewett, an inspiring leader, passed away this past week after battling Motor Neurone Disease.