World No.2 Roger Federer joked that he had some dodgy help from the person running Hawk-Eye after helping guide Switzerland to victory over Russia at the Hopman Cup.
Federer gave his nation a 1-0 lead after beating Karen Khachanov 6-3 7-6 (10-8) in front of 13,943 fans - a record crowd for the mixed-teams event.
Belinda Bencic secured the tie win for Switzerland with a 6-1 3-6 6-3 win over Anastasia Pavlyuchenkova in match that almost lasted two hours.
The result means Switzerland and the US will battle it out for a spot in the final when they meet on Thursday night.
Federer's singles match was on a knife's edge during a pulsating second-set tiebreak.
The 19-time grand slam champion saved a set point, before eventually prevailing on his third match point when he successfully challenged a Khachanov winner.
The 36-year-old thought the shot was in and was only challenging in the unlikely chance he was wrong.
To his surprise, Hawk-Eye showed the ball had sailed wide by the barest of margins, with Federer having a chuckle to himself after being awarded the win.
"I thought it was in," Federer said.
"When I looked at the mark on the floor, I thought it actually touched.
"And then when it went out, it was almost a bit of a surprise.
"It almost felt like somebody in the back said, 'Let's get this match over, we need Roger to win this one'."
Khachanov took the decision on the chin.
"I mean what can you do? You have to put this ball inside the line. Next time," Khachanov said.
"You just hope that it was in or it was touching the line. But you cannot do anything. Maybe Hawk-Eye was wrong.
"I mean, it's tough to say. I was hitting. I didn't see if it was in or not. I was hoping it was in."
Federer is due to meet Jack Sock on Thursday night in the men's singles rubber.
But the American is under an injury cloud after retiring from his match against Japan's Yuichi Sugita on Tuesday with a hip problem.
Federer started his Hopman Cup campaign with a straight-sets win over Sugita.
Although Federer was broken in his first game against Khachanov, he quickly bounced back to win the opening set in 29 minutes.
The second set was an entertaining arm wrestle as both players produced powerful service games.
But Federer finally cracked the Russian in an epic tiebreak.
"It was good to play a tiebreaker of this kind early on in the season," Federer said.
"Just to get through these nervy situations with the pulse up high, and you're sweaty, and you're trying to figure it out.
"It was a good match overall. I was very happy with my performance. I thought the intensity was great."