Melbourne, Jan 19 (IANS): The Australian Open debutant Jenson Brooksby staged an upset in the second round after beating second seed Casper Ruud to extend his dream debut here on Thursday.

For the second day running at the Australian Open, an unseeded American has bounced a top seed from the men's singles draw. After Mackenzie McDonald's shock win against Rafael Nadal on Wednesday, Jenson Brooksby defeated Ruud 6-3, 7-5, 6-7(4), 6-2 on Thursday to enter the third round.

With the defeat, Ruud misses out on his chance to leave Melbourne atop the ATP Rankings. Either Novak Djokovic or Stefanos Tsitsipas can claim World No. 1 by winning the Australian Open title, with the injured Carlos Alcaraz set to remain on top with any other outcome.

Next up for Brooksby is countryman Tommy Paul, who booked his third-round place with a 6-2, 2-6, 7-6, 6-7(4), 6-3, 6-4 win against 30th seed Alejandro Davidovich Fokina.

The Melbourne debutant, Brooksby, was in control throughout the match, with Ruud having to save three match points and battle back from 2-5 in the third set just to extend the contest.

Brooksby scored the biggest win of his career by frustrating the two-time major finalist, using a steady diet of crosscourt backhands to keep him pinned to his weaker corner for much of the three-hour, 55-minute match.

After the second set, Ruud left the court for a medical timeout. The World No. 3 dug deep to force a fourth set but was outclassed in the decider.

"First and foremost, Casper is a warrior. I knew it would be a great battle out there. I was pretty confident with my level and just wanted to have fun competing out there," Ruud said post-match.

"I was just really proud of my mental resolve there after the third-set battle didn't go my way, to just turn it around."

"I had to] just keep bringing my level," Brooksby said of his mentality after dropping the third-set tie-break. "I thought I was playing really strong and I just wanted every game to not lose my focus out there."