Rock bottom Rovers were the better team in the first half at Priestfield but ultimately failed to find the net for a seventh game out of 12 in the league.
The Gills upped the ante after the break and their pressure paid off when Vadaine Oliver headed home a late corner to seal a 1-0 win.
"We had a routine and after so many corners we changed it to an outswinger and I had to remind Lloydy before he took it, but he took it and V got on the end of it,” said Evans.
“Doncaster players were all standing there at the back stick and on the line waiting for an inswinger.
“It was the first time we varied it up and I think the Donny boys got caught out. They went running to the referee, I don’t know what for, it was a simple corner and a simple header.
"They were nowhere near Stuart or V. I had said to Paul Raynor (the assistant manager) we have to change it. We shouted to Kyle Dempsey (the captain), after the previous corner, and he has given the instruction to Lloyd. We said 'let’s do the outswinger and let’s see if we can find V or Rhys Bennett.' We found V.
“That was a good tactical decision implemented brilliantly with a good ball in from Lloydy and a great header from Vadaine and then it is always going to be a bit nervy in the last few minutes.”
He added: “Second half was more like us, more intense, more on the front foot and the disappointing thing is we didn’t get the chance to relax by getting the second goal.
“I wasn’t pleased with the first half and people could probably hear me in the seats when I was in the dressing room at half time. I just thought we had lacked all that intensity and willingness to run that five yards at maximum speed that we had against Sunderland.
“I said that if we disrespect Doncaster we lose the game, we were sitting there 0-0 and we had an opportunity to win the game.
"We changed the style of play and system, went three up front, we asked Adshead to pass it and keep control of possession at times. I think second half Adshead, O’Keefe and Dempsey were brilliant, Danny Lloyd was excellent and from the big two up front we got a real shift."