After missing two and a half months with a back injury, Williams made her return to the tour last week in Toronto, falling first round to Kirsten Flipkens - but this week she turned that result right around, falling behind 4-2 in the first set but reeling off eight games in a row to take complete control against Cepelova, blasting one last crosscourt forehand winner to finish off the Slovakian qualifier, 64 61.
"I had a slow start. I was missing shots but I was being aggressive, so I realized if I had made a few more shots that it would probably go the other way for me," Williams said. "But I thought she was really determined out there. She just looked really determined and really energetic. She was definitely going to take it to me, so it was good to turn it around and get the win. It feels good to win tonight."
It was actually Williams' first match win since a Fed Cup win over Johanna Larsson in late April.
"My matches have been pretty spaced apart," Williams said. "It doesn't really give you a chance to get a rhythm. That's what I'm looking for. For the remainder of this year, hopefully I'll just play a lot of matches and have those situations where I'm up 40-15 or down break point in a tie-breaker, just kind of getting that feeling again. I have a lot of experience, but a lot of rustiness right now as well."
Perhaps fitting is that Williams' second round opponent could be the No.13-seeded Flipkens again.
Williams' contemporary, Martina Hingis, made her doubles comeback a few weeks ago and was also among the winners, partnering Daniela Hantuchova for a 46 64 105 victory over Anabel Medina Garrigues and Flavia Pennetta. Medina Garrigues and Pennetta led 64 31 with points for 64 41.
Back to singles, Alisa Kleybanova - a former Top 20 player who returned to WTA competition last week from a long time away fighting off Hodgkin's lymphoma - got the first WTA-level match win of her comeback, scraping by Sofia Arvidsson, 46 64 76(7). Kleybanova never faced match point but did have to come from 5-3 down in the third set, and she was two points away from losing a number of times.
The highest-ranked player in action was No.9 seed Angelique Kerber, a finalist here last year, who dropped a marathon first set after holding set point but then needed just 48 minutes to storm through the next two sets, running away with the match against Italian qualifier Karin Knapp, 67(6) 60 61.
"The first set was a little bit tough for me because I couldn't find my rhythm and she was playing well in the important moments," Kerber said afterwards. "But after the first set I was just trying to change my game a little bit and play a bit more aggressive, not moving too much around and far from the line.
"Of course when I came here I had a lot of good memories from last year. I feel a little bit of the pressure, of course, but I'm just trying to enjoy every moment because I love this tournament."
The other two seeds in action during the day session won as well, though one had it far tougher than the other. No.11 seed Samantha Stosur served up a storm, never facing a break point en route to a 61 75 win over Svetlana Kuznetsova - meanwhile, No.16 seed Maria Kirilenko battled almost three hours to beat Georgian qualifier Anna Tatishvili, 46 76(4) 76(4). Kirilenko blasted 12 aces in the match.