Australian off-spinner Lyon's Ashes series looked over when he sustained a serious calf injury while fielding on Thursday.
But he surprised virtually everyone in the ground when he hobbled out to bat at number 11 as his side looked to add more runs to their lead over England.
What followed was one of the most bizarre innings ever seen at the famous old ground.
Batting in partnership with fast bowler Mitchell Starc, Lyon, playing in his 100th consecutive test match, looked like a sitting duck as he fended off some hostile bowling.
Remarkably, despite being on one leg, he played some cultured shots but was unable to run between the wickets - meaning he and Starc's only option to add to the score was to try and hit boundaries.
At one point Starc was denied a six by a stupendous piece of fielding on the boundary by England substitute fielder Rehan Ahmed, and in the confusion Lyon somehow managed to hop between the wickets to complete a single before collapsing in a heap.
In the end, Lyon faced 13 balls, scoring a boundary and sharing in a partnership of 15, including a booming Starc six, that allowed Australia to set England a formidable 371 victory target - 12 more than the Ben Stokes-inspired England successfully chased in 2019 at Headingley.
In true Aussie fashion, Lyon said he had no hesitation in taking one for the team.
"I wanted to bat. It was my call," Lyon said. "I knew the risks but I'd do anything for this team and you never know how big a 15-run partnership can be in an Ashes series.
"I'm proud of myself for going out there and doing that. If it was tomorrow I'd do it again, and again and again and again."
Lyon said he had exchanged a few words with England bowler James Anderson before shuffling out to the square.
"He asked me am I stupid," Lyon said. "And I said yes."
Lyon's exploits certainly inspired Starc and captain Pat Cummings who between them reduced England to 45-4 before the hosts closed on 114-4, needing 257 runs for victory on day five.
