The 26-year-old Peniston, playing in his first ATP Tour main draw, won two tie-breaks to beat the world number five 7-6 (7/4), 7-6 (7/2).

Norwegian Ruud, a clay-court specialist, struggled with his timing throughout and also needed treatment on a hip after taking a tumble on the baseline.

Peniston, ranked 180th in the world, won five points in a row on his way to taking the first-set tie-break, not long after Ruud had slipped on set point.

Ruud took another tumble early in the second set but broke Peniston for the first time for 4-3, only for the home hope to hit straight back before completing the job in another tie-break.

Peniston, who has a Wimbledon wildcard, survived cancer as a baby before going on to join the professional tennis ranks after learning his trade in France and at the University of Memphis.

“I can’t really believe it, it feels like a dream,” he said. I didn’t get much sleep last night, it doesn’t feel real.

“I’ve been playing well. Obviously Casper is an unreal player, he did so well at the French Open so I knew it was a tough ask, but you have to step on the court knowing you’ve got a chance to win. So, that’s what I did.”

When he was just one year old Peniston was diagnosed with rhabdomyosarcoma, a soft-tissue cancer, and needed surgery and chemotherapy as well as regular check-ups for years afterwards.

“It was definitely a difficult start to my life,” he said. “I don’t remember much. But for my parents and my brothers, I think it must have been a pretty, pretty tough time.

“But I had the amazing, amazing doctors and amazing nurses who helped me through that – and my family, huge, huge thanks to them.

“And yeah, standing here today, that was pretty good.”

Defending champion Matteo Berrettini beat Britain’s Dan Evans 6-3, 6-3, restoring order after all four of the other top five seeds fell victim to first-round upsets.

The Italian, fresh from winning his sixth ATP Tour title in Stuttgart, claimed the 2021 Queen’s Club title before reaching the Wimbledon final, finishing the grass season with an 11-1 record.

“I love to play on grass,” he said. “I love to play here. I got a (hand) surgery a few months ago and I didn’t know if I was able to play this grass season so I’m really thankful to be here.”

Three-time Grand Slam champion Stan Wawrinka celebrated the news he has been handed a wildcard to Wimbledon with a 7-6 (7/2), 6-7 (6/8), 7-6 (7/5) win over American Frances Tiafoe.

Wawrinka has not played at the All England Club for three years as he battles back from two foot surgeries.

Earlier, US player Sam Querrey beat fifth-seeded Argentine Diego Schwartzman 6-1, 6-4.