Bouchard, who made a fairytale run to her first Grand Slam semifinal here a year ago, seemed headed for a very routine win as she surged ahead 6-1, 3-0 in about 40 minutes. But Begu, who was having the best Grand Slam of her career, snapped into form from there, winning five games in a row to lead 5-3 and, after Bouchard caught up to 5-all, sneaking out two more games to push it to a decider.
But that decider was all Bouchard, as the No.7-seeded Canadian cruised to a 6-1, 5-7, 6-2 victory.
Bouchard is now through to the quarterfinals of a Grand Slam for the fourth time, and it's turned out to be quite a lucky round for her - every time she's gotten this far she's gone at least one round further, reaching the 2014 Australian Open semifinals (losing to Li Na), the 2014 French Open semifinals (losing to Maria Sharapova) and the 2014 Wimbledon final (losing that one to Petra Kvitova).
Bouchard was asked about the second set turnaround in her post-match press conference.
"It's disappointing because I want to play so well and I want to be so perfect, but that's not possible. But it happens," Bouchard said. "I think I started being a bit less aggressive, a bit too passive, and that's not my game at all. I don't do well when that happens. She strung together a few good points and hit some good shots and serves, and she got some more confidence as the second set went on.
"It's disappointing, but I learned from it and I'll make sure it doesn't happen next time."
Did Bouchard do anything special in between the second and third sets to regroup?
"I've played a few matches on Rod Laver Arena and I was just able to breathe and kind of relax in between the second and third and just refocus. I had the confidence in myself that was like, 'Okay, I can't change the past.' I told myself that. 'As much as I want to, I can't change the second set.'
"But I just tried to go back out there and do better in the third set. That's what really motivates me. I want to be so good that if it's not good, I'm so motivated to try and show that I can do better."
Awaiting Bouchard in the quarterfinals is No.2 seed Maria Sharapova, who beat No.21 seed Peng Shuai later in the day. Read more about the Sharapova-Bouchard quarterfinal match-up here.