Play resumed under the afternoon sun with Sharapova leading 4-1 in the first set after heavy rain and lightning forced organizers to suspend the match late Monday following a three-hour rain delay.
Sharapova, making her first Rogers Cup appearance since 2014, picked up where she left off Monday. She won six straight games after the restart and needed only 36 minutes to win the second set.
The 31-year-old had three aces and only committed two double faults to her opponent’s 11.
The Russian is 5-0 all time against the 229th-ranked Karatantcheva, who was playing in her first WTA main draw in more than a year.
Ostapenko, the 11th seed in Montreal, committed 10 double faults while struggling with her serve as she was eliminated in the first round at the Rogers Cup for the third straight year.
Konta had eight aces while committing just three double faults.
“Because of the back and forth in that first set, after that what I did well was I settled down,” said Konta, the former world No. 4. “I played myself into the match and tried to be as tough as possible.
“She has such a big game, so many big shots, sometimes you are spectator out there. When I had the opportunity to do the most I could, stay strong, I think I built up enough momentum. That’s why I was able to keep pushing through in the second and third.”