Watt came on at the start of the second half for Miku and nine minutes later he was in the right place and the right time (again) to bundle a Mulgrew cross over the line from the far post.
And he wasn’t the only Hoops player to show the same prowess which led to that 2-1 win over Barcelona.
Fraser Forster pulled off a stunning one-handed save.
But he could do nothing a minute later when St Johnstone striker Nigel Hasselbaink fired in the equaliser.
Bayal fired in a cracking shot with ten minutes left but it went just over the bar as Celtic pressed for a winner.
But the Hoops failed to find a second goal and remain in second place in the league after Hibernian won earlier today.
“There was no spark,” said Lennon afterwards, citing the hard work of last Wednesday.
“You’re looking for that wee spark and Tony gave us that but some of them are dead on their feet [in the dressing room].
“It’s the second time in two weeks now we’ve taken a lead and conceded it and that’s disappointing.
“We rested them as best we could. Mentally, I’m sure the game [against Barcelona] took a lot out of them. There’s no doubt the physical side of it, they are sort of struggling with it a wee bit at the minute.
“The players that played the other night gave us everything again but there was just that bit of flatness about us. I accept that but I’m not happy about it.
“The squad’s getting stretched but that’s not an excuse and we have already played maybe nine, 10 games more than any other team in the country.
“St Johnstone have had a full week to prepare for this game. We’ve had half a day.
“While it’s difficult, I’ve got the players to be able to cope with that but they’re just suffering a little bit from mental and physical fatigue.”