(CNN) -- Serena Williams was extended to three sets by one of the next generation of stars hoping to assume her No.1 mantle before advancing to the third round of the WTA event in Cincinnati Wednesday.
19-year-old Canadian Eugenie Bouchard is ranked 62nd in the world but showed enough to suggest she will be aiming higher very soon.
She took the opening set 6-4 before Williams turned the match around in her trademark fashion to level a one set apiece.
Bouchard, who beat former World No.1 Ana Ivanovic at Wimbledon this year, kept battling but Williams had too much experience to run out a 4-6 6-2 6-2 winner in one hour 47 minutes.
Williams is coming off winning the title in Toronto at the weekend as she continues her dominant form on the WTA this season.
Only surprise defeats at the Australian Open to Sloane Stephens and at Wimbledon to eventual runner-up Sabine Lisicki have interrupted her winning run and she will be heavy favorite to defend her U.S. Open crown later this month.
Fellow American Stephens shocked World No.3 Maria Sharapova Tuesday at the hard court tournament in Ohio where top billing is shared with the ATP event.
Serena's older sister Venus Williams' disappointing 2013 season continued as she lost in three sets to world No. 23 Elena Vesnina.
Williams missed Wimbledon due to a back injury and has not a WTA title since the Luxembourg Open in 2012.
Fifth seed and defending champion Li Na recovered from a slow star to eventually beat American wildcard Lauren Davis 4-6 6-1 6-1, while No. 4 Agnieszka Radwanska won 10 games in a row to overcome Uzbekistani-born American Varvara Lepchenko 6-4 6-0.
World No.2 Andy Murray got his campaign in Cincinnati off to a winning start with a 6-2 6-3 victory over Mikhail Youzhny of Russia in an earlier match.
The Wimbledon champion had lost his third round match at the Montreal Masters last week on his return to the circuit after his historic triumph, but made no mistake here.
The 26-year-old Scot broke service five times on his way to victory in just 70 minutes.
It extended his career record against Youzhny to 4-0 having beaten him in the fourth round at Wimbledon.
Murray has won the Cincinnati trophy twice, beating Novak Djokovic both times in the final.
"I think it's important for me to try to get a few matches this week, if I can," Murray told the official ATP Tour website.
"I did what I wanted to do and got through the match."
He was joined in the third round by top seed Novak Djokovic, who beat Juan Monaco of Argentina 7-5 6-2.
The Serbian is bidding to complete his set of the nine Masters 1000 titles this week, coming off the back of a semifinal loss to returning Rafael Nadal in Montreal.
Twelve-time grand slam winner Rafael Nadal is also safely through after a straight-forward 6-2 6-2 defeat of world No. 100 Benjamin Becker.
Veteran German Tommy Haas earned a third round match against Roger Federer after beating Marcel Granollers 6-4 6-1 in 74 minutes.