American Jenson Brooksby caused the second big shock of the Australian Open by knocking out second seed Casper Ruud to reach the third round.

A day after Rafael Nadal limped to defeat against another American, Mackenzie McDonald, Brooksby beat Norwegian Ruud 6-3 7-5 6-7 (4) 6-2 for the biggest victory of his career, recovering from missing three match points in the third set.

The result means the men’s event has lost its top two seeds before the third round for the first time at any grand slam since 2002.

Ruud would certainly have had higher hopes for the tournament having reached two grand slam finals last year, at the French Open and US Open.

But he struggled from the start with the unorthodox style of 22-year-old Brooksby, who is named after former British racing driver Jenson Button.

He had reason to curse his luck, too, after losing the second set when a shot from Brooksby hit the tape and dribbled over the net.

Ruud then took an off-court medical timeout for an unspecified ailment and was clinging on by his fingernails at 5-2 down in the third but Brooksby was unable to serve it out, blinking at the finish line in agonising fashion.

Ruud looked like he might turn the match around when he took the tie-break, with Brooksby beginning to struggle physically, but he forged ahead again and finally clinched his fifth match point.

He raised weary arms in the air, and then said: “I was really proud of the mental resolve after the third set didn’t go my way.”

It has been a hugely successful tournament so far for the American men, and Brooksby was joined in the third round by Tommy Paul, JJ Wolf – who upset seeds in Alejandro Davidovich Fokina and Diego Schwartzman, respectively – and 20-year-old Ben Shelton, who is on his first ever trip outside the US.

Fifth seed Andrey Rublev also advanced, defeating Emil Ruusuvuori 6-2 6-4 6-7 (2) 6-3 to set up a third-round clash with Dan Evans.