TORONTO, Canada -- No.8 seed Serena Williams looked sharp in her first match since the Wimbledon final, as the American eased past World No.20 Elise Mertens of Belgium, 6-3, 6-3 on Wednesday night, to advance to the third round of the Rogers Cup.

"I feel like my movement is great -- been working on my fitness, so I felt like it really was able to shine through today," Williams said, in her post-match press conference. "I'm loving going out there, and I'm loving kind of running. So it's a good thing."

23-time Grand Slam champion Williams picked up her third Top 20 win of the season after an hour and a quarter of play against Mertens, as she seeks the fourth Rogers Cup title of her career. Williams, who won the event in 2001, 2011, and 2013, improves her win-loss record at the tournament to a staggering 31-4.

Read more: ‘Pain-free’ Serena looking for ‘momentum’ in Rogers Cup return

Williams had 19 winners to Mertens's 11, and she broke the Belgian five times out of her 10 break points. Williams fired five double faults during the clash, but Mertens had eight double faults. The Belgian had 19 unforced errors in the tilt in total.

"Now that I'm just injury-free, I'm just enjoying being able to train, and I haven't been able to do it since January, really," said Williams. "So I just think that the fact that I can train and practice and get in the gym is really going to be helpful for me."

Mertens took the early lead in the encounter, breaking for 2-1 after Williams misfired a backhand into the net on break point. However, thunderous serving by Williams in her next service game signified an uptick in her play, and she kept the momentum going from there by breaking back to reach parity at 3-3.

"I know when I got down one break I got real negative," said Williams. "I don't know what happened on the first time I got down. I think [Mertens] just played really well. She's obviously a really good player. So, yeah, I just needed to just double down and get more focused."

After pulling through a tricky four-deuce service game, finally holding with an ace for 4-3, Williams took command of the opening frame by wresting Mertens’s next service game out of the Belgian’s hands from game point up. Now up a break at 5-3, Williams used more solid serves to pull herself back from 0-30 down and obtain the one-set lead.

Mertens again took an early lead in the second set, as she broke Williams for a 2-0 advantage. But, as in the first set, the lead was short-lived, as Williams broke back in the very next game, pulling back on serve via a blistering backhand winner down the line.

Williams started to pull away when she broke Mertens for a second straight time, after the Belgian double faulted on the fifth break point of a pivotal game. Later, at 4-3, Williams again used stupendous serving to get out of a 0-30 deficit and hold serve, putting herself one game away from victory.

Serving at 5-3, Mertens fired a forehand crosscourt winner to reach double game point, but those were squandered, the second with another double fault, and after two deuces, Williams reached match point with a stunning, error-forcing return. There, Mertens hit a forehand miscue long, and Williams had picked up another match-win in Canada.

Next up for former World No.1 Williams will be Russian qualifier Ekaterina Alexandrova, who defeated Zhang Shuai of China, 6-4, 6-3 earlier on Wednesday. It will be the first meeting between Williams and 48th-ranked Alexandrova.

"I face a lot of players for the first time, so it's just really about going out there and doing a little studying about their game and then going from there and playing," Williams stated.