The Canadian wasn't at the incredibly high level that he has performed at in the last few weeks, a spell which saw him win three back-to-back titles.
Auger-Aliassime was put under huge pressure by an inspired Ymer, and at one point was staring down the barrel at 7-6(6), 4-1 down. He was second-best for the majority of the contest up until that point, and couldn't contend with the shotmaking of the talented Swede. Incredibly, the break of serve at 2-1 in the second set was just the first time he had been broken in his last 94 service games.
However, the world number eight reeled off seven games in a row to take the second set 6-4 and go a break up in the third, with the momentum seemingly shifting.
But Auger-Aliassime was soon broken back, and the final set was a total rollercoaster. Both players were producing winners at will, with Ymer refusing to give in after going behind on several occasions.
A tie break was the only way to separate the pair, and following some scintillating rallies and nail-biting tension, Auger-Aliassime secured a (6-7(6), 6-4, 7-6(6)) victory on his second match point, as the match timer hit three hours and 31 minutes.
Impressive character and fight to mount such a comeback, further emphasised by his calmness at the big moments. Despite not being at his best, he saved 14 of 17 break points and often upped his level when it really mattered.
Targeting a spot in the ATP Finals, the equation for Auger-Aliassime before the tournament was simple. As long as Taylor Fritz or Hubert Hurkacz don't win the Paris title, he would qualify. This was made even more intriguing by the fact that he could be set to meet the former in the third round.
For the first set and a half, it looked like he would have to be relying on other players. Ymer's carefree and relaxed demeanour had clearly loosened him up, and he was on the front foot for most rallies. After a tiebreak where Auger-Aliassime made a number of mistakes, Ymer took the lead and surged ahead in the second set, before the match flipped on its head.
"Somehow I found a second wind after saving those break points at 4-1,” said Auger-Aliassime - who made 22 unforced errors in the first set
“I played better and better, coming through the court much better, serving better. It was pretty epic. Three hours and 30 minutes on the court, quality rallies. He was making me work all the time. Definitely a win to remember.”
This is Auger-Aliassime's fourth tournament in four weeks, and he is currently on a 14-match winning streak. However, he made it clear that he would not complain about potential fatigue.
"[I’m pretty tired], but it's not the time to complain and whine,” he said. “I decided to play these events, I won three of them, so I can't complain. It's fantastic.
"Here, I'm just trying to give my best. Let's go and see day-by-day how I feel. Definitely today was a tough one, not only just the game but the way he was playing as well, he was making me work a lot. That added extra toughness to the match.”
Auger-Aliassime will now be looking ahead to what could be a critical clash against Fritz in the third round. However, the American will have to pass home favourite Gilles Simon first, who has extra motivation in what is his last-ever tournament before retirement.
