Jessica Pegula was pushed all the way in her opening match of the Canadian Open by Maria Sakkari, but got herself over the line to reach the second round.
Pegula, who is the defending champion in Montreal, saved five set points in the opening set on her way to a 7-5 6-4 triumph in one hour and 32 minutes on Wednesday.
The American came into the game off the back of consecutive first-round defeats at Wimbledon and the Washington Open, and appeared set for another early exit here.
The third seed broke Sakkari in the third game of the first set, only for her opponent to roar back and win the next four as she got the better of Pegula's serve.
And while Pegula broke back, Sakkari had the chance to serve for the first set, but was unable to take her opportunity as the world number four managed to keep herself alive.
Pegula made the most of her reprieve by breaking Sakkari in the next game before closing out the set by holding to love, which took the wind out of her opponents' sails.
The two-time champion opened the second set with a break before doing so again in the fifth game, though Sakkari returned the favour shortly after.
But Pegula remained composed and sealed the win with a perfectly placed forehand winner, setting up a clash with Latvia's Anastasija Sevastova in the next round.
Data Debrief: Pegula's Montreal three-peat lives on
Pegula looked set to be the first defending champion at the Canadian Open to lose their opening round match in the women's singles since Caroline Wozniacki in 2011, but she found her groove to kickstart her title defence.
While being put through her paces by Sakkari, Pegula has now won seven WTA-level main draw matches against the Greek, the joint-most she has managed against a single opponent in her career so far (also seven against Camila Giorgi).
Her victory also saw her pick up her 18th win from 20 matches in the women's singles at the competition. Only Monica Seles (19/20) has registered more wins from her first 20 matches at this event during the Open Era.
