Prior feared he was gone for a second-ball duck at Lord's, and would have to deal with the potential consequences. Instead, he was reprieved by a marginal umpire's call - his back leg not quite in line with off-stump - escaped the lbw review by Sri Lanka spinner Rangana Herath and went on to make 86 in a sixth-wicket stand of 171 with double-centurion Joe Root.
England, thanks mostly to Root's unbeaten 200 but also the contributions of Prior and several others, piled up their highest Test score against Sri Lanka.
They subsequently discovered it will be no easy task to beat the tourists in this first Investec Test, after opener Kaushal Silva (62 not out) helped the visitors to 140 for one at stumps on day two in reply to 575 for nine declared.
England nonetheless remain the front-runners, and for 32-year-old Prior, recalled after being dropped last winter and despite the clamour from many for Jos Buttler to play instead, there has been vindication.
For almost two minutes on Thursday evening, though, he admits time stood still as his short and long-term prospects were decided by others.
"You're just watching the screen, and it's like 'that looks dead'," he said, of the moments after Herath beat his forward lunge. "I'm thinking 'right, that's nought off two balls - see you later, Matt!' Then, when the umpire's call came up, I almost looked at Rooty and said: 'Right, it's changed. I'm back. Here we go.' I decided to attack again, and hit that one over the top. That was me off and running, and I felt comfortable from then."
Even before his early scrape, there had been plenty of nerves for Prior, in returning to a high-stakes game, at the same ground where he made a century on Test debut.
"It was very similar to 2007, coming here for the first time, those initial nerves," he continued. "I suppose the way I look at it, this is the third part of my career - and I'm pretty keen to see how far I can go with that.
"It's a really exciting time, and I'm absolutely passionate about playing cricket for England."
Did he worry then, before he was named in the squad at the start of this Test summer, that his time as an international cricketer might be up?
"More through the injury," he admitted. "I thought it was touch-and-go for a while, and it wasn't improving. But having worked tirelessly to try to make sure I was in a position to declare myself fit, I felt confident I might get another go."
Prior could add only 10 runs on day two, before succumbing short of an eighth Test hundred. Root took on the mantle. For Sri Lanka, a long road still lies ahead to avoid defeat.
Dimuth Karunaratne, the opener who survives the night said: "It's a flat wicket, and we hope Kaushal and Sanga can go on tomorrow."