Rafael Nadal called his three-set defeat to Denis Shapovalov in Montreal his toughest defeat of the season so far.
The Spaniard fell to the 18-year-old Canadian in front of packed stands, having won the first set and being up a mini-break in the third-set tiebreak.
"Probably my worst loss of the year, because I lost against a player with a lower ranking," he said. "At the same time because of the opportunity I had here to come back to the No. 1. Always tough, but the draw was not that impossible after all the matches that were happening."
Nadal said he allowed his opponent to take charge. "I didn't [go] for the shots. I didn't [feel] the ball tonight," he said. "I make too many mistakes in important points. In all terms, I cannot be happy about the things that I did."
But he also praised Shapovalov, who is now ranked No. 143 and was the 2016 boys champion at Wimbledon.
"He has a great potential," Nadal said. "He has everything to become a great player. He played with the right determination in the important moments."