A goal down and struggling to make a big impression on the Bolton resistance, Glenn gambled with his formation and drafted in Les Ferdinand and Goran Bunjevcevic for Chris Perry and Steffen Freund.
Within two minutes of the re-start a 1-0 deficit quickly turned into a 2-1 lead.
"I didn't know they would work out that quickly into the second half!," admitted Glenn. "But we looked at giving ourselves a second option, we looked to try and play balls in and around the penalty area.
"We didn't have enough good movement in the first half and I just felt we needed a second option. We took a chance, we just left two at the back. We left Simon and Christian as wing-backs, with Gus and Teddy just behind Sergei and Les.
"It was a big risk, if they had scored a second goal first it would have been downhill from there. But it paid great dividends.
"They played so deep that we needed that second option of the diagonal ball into the box. It worked so quickly, Les pulled off lovely, great ball from Darren, and Gus scored off the bar - good reactions.
"That got us going, my first thought after we scored was that it was a bit like Manchester United scoring so early in the half against us when we were three-up. I just felt 'yeah, we can take it on from here'.
"The second goal Goran played a fantastic part in, he's got that ability to play a pass to unlock the door. That's why we put him on and it worked a treat for us.
"Bolton came back at us again with great character, then we showed a lot of character.
"Credit to everybody, it was a lot of hard work."
Glenn's inspired double change at half-time altered the course of the game against Bolton, but even the boss didn't expect it to happen so soon.