Federer's rollercoaster of emotions amid Hawk-Eye dramas

Roger Federer went through a raft of emotions during his Hopman Cup clash with Karen Khachanov, leaving the crowd in hysterics.

Federer gave Switzerland a 1-0 lead after beating Khachanov 6-3 7-6 (10-8) on Tuesday night, and he profited from some fortunate calls from Hawk-Eye.

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The World No.2 had the crowd cracking up early in the second set when Khachanov challenged an out call off his racquet, but hawkeye took an agonisingly long time to reveal the correct decision.

With the players and spectators eagerly awaiting the replay, Federer quipped: "I can't take it, it's too nerve-wracking", sparking laughter around Perth Arena.

The Swiss legend later joked that he had some dodgy help from the person running Hawk-Eye after another incredibly close call on match point.

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."

with AAP