The Englishman had just shot 4-under 67 and had moved to 1-over par, and into contention in the 132nd Open Championship.
Fifteen minutes later, he got some of the worst news of his professional life.
Roe was informed, after doing a television interview, that he and playing competitor Jesper Parnevik (81) had been disqualified after signing incorrect scorecards.
In this event, players are given their own scorecard before the round and are expected to exchange them on the first tee before keeping one anothers score.
Roe and Parnevik did not exchange cards. Therefore, Parnevik kept Roes score on his own card, and Roe did the same.
Despite a lengthy stay in the scorers tent after the round, the mistake was not noticed. And when the two left the premises, after each signed the incorrect cards, they were automatically disqualified.
'I spent plenty of time in the hut. I didn't rush in and rush out. Obviously after having a good day I'm going to double and triple check my scores,' Roe said. 'It's unfortunate that no one noticed. But there's no one else to blame but myself.'
Roe could have accepted Parnevik's score of 81 -- since that is the one he signed -- if all of Jesper's scores had been equal to or higher than Mark's. But Roe made a 5 at the par-5 fifth, while Parnevik had a 4.
Had they not signed their cards, they could have changed all the numbers appropriately.
'I just feel terrible for Roe. He was playing so well. It's just not fair,' said Parnevik, who was at 15-over par. 'It's a dumb mistake but it shouldn't be the end of the tournament.'
Said chairman of the R&As Championship Committee David Pepper: 'I think sometimes the punishment might appear too harsh, but one has to sit down and write a set of rules and you have to abide by those rules.'
Despite the incident, Roe said he will take great memories from Saturday's round.
'I learned alot about myself. I'm playing well again. I enjoyed the crowds. I enjoyed the attention. It was a real thrill. And I'm going to think about that rather than the disqualification,' he said.