Casper Ruud reached the US Open semi-finals for the first time on Tuesday, potentially reigniting his bitter feud with Nick Kyrgios whom he once described as an "idiot".
The Norwegian fifth seed defeated Italy's Matteo Berrettini 6-1, 6-4, 7-6 (7/4) to make his second Slam semi-final of 2022 having finished runner-up to Rafael Nadal at the French Open.
Wimbledon finalist Kyrgios faces Karen Khachanov later Tuesday in his quarter-final.
Fiery Kyrgios and Ruud fought an ugly war of words when they met at the Rome Masters in 2019.
Kyrgios was penalised a game for swearing at a line judge, threw a chair onto the court, packed his bags, stormed off and was defaulted.
He was later fined 20,000 euros and docked ranking points. Ruud called for Kyrgios to be banned for six months, branding his rival an "idiot".
Kyrgios responded by describing the Norwegian's tennis as "boring" and accusing him of "stealing" points by playing in a succession of low-profile claycourt events in order to boost his world ranking.
"You never know what's going to come out of his racquet or his mouth," said Ruud on Tuesday.
- 'A bit tense' -
"On the personal note, there is not that much of a relationship. I mean, we didn't say hi in the locker room for some time, but we do now, so it's better.
"There were a time where it was probably a bit tense after things were said back and forth, but he actually came to me in Laver Cup last year and congratulated me when I won my match, which was nice."
Kyrgios, who knocked world number one and defending champion Daniil Medvedev out in the third round, is attempting to become the first Australian man to reach the US Open semi-finals since Lleyton Hewitt in 2005.
Khachanov is playing in his third Slam quarter-final but has yet to reach a semi-final.
"I think Nick has taken steps as a player. We all know he's been a huge talent but this year he has proved he can win many matches in a row and it is impressive," Ruud said in his on-court interview.
"Obviously he has improved and he will be a dangerous player for sure. Let's see if it will be some drama or not, but I'm ready for anything."
Ruud broke Berrettini five times in Tuesday's clash while saving seven of nine break points.
He raced through the first two sets under the roof of Arthur Ashe Stadium before 2019 semi-finalist Berrettini stopped the rot with a break for 2-0 in the third.
At 2-5 down, the 23-year-old Ruud saved two set points before recovering and going on to dominate the tiebreak.
"It was a better start to a match than I ever had before. Everything was going my way plus Matteo didn't serve as well as he usually does," said seventh-ranked Ruud who could finish the US Open as the new world number one.
"I got a little nervous towards the end of the second set because things were going a little too well.
"You think you can walk on water, which is not possible. The third set was very tough."
Berrettini, who missed the French Open because of a hand injury and Wimbledon due to Covid, admitted he had endured a day to forget.
"Nothing more I can say than the worst day of the tournament probably in the most important moment," he said.