The visitors took the lead with an excellent move in the tenth minute, which was capped off by James Constable’s crisp strike.
It was an advantage they held until six minutes from time, when John-Joe O’Toole headed in an equaliser.
Lewis rued United’s inability to build on the lead and provide a cushion before Rovers’ late onslaught.
“Because we have been ahead, the lads are really gutted and see it as two points dropped,” the caretaker manager said.
- Josh Ruffels and Danny Rose show their frustration as Ruffels misses a good chance
“If you’re a goal up you expect to try and hang on and perhaps we should have made it 2-0.
“We had a spell in the second half where we were quite dominant, but Bristol Rovers were always going to come at you while it was 1-0.
“With 15 minutes to go you are always going to be under pressure, but if we had made it 2-0 perhaps that would have killed the game off.”
The home side came into the game strongly late on, as the visitors were pinned back.
Lewis was critical of the way United conceded several set-pieces in dangerous areas, one of which led to O’Toole’s equaliser.
But he felt the change in the balance of play owed more to the hosts playing well, rather than his side tiring.
He said: “We didn’t want to step back and I think you have to give credit to Bristol Rovers.
- Deane Smalley shows close control despite losing his footing
“I would be disappointed if we were 1-0 down at home and we didn’t have the away team on the back foot.
“If you go anywhere in the league that will be the same.
“Perhaps we didn’t keep the ball as well as we could’ve done in the last ten minutes, but I thought we were comfortable enough until they scored.
“We had a couple of iffy moments right at the end, but I think it would’ve been unjust to lose the game.”
One boost to come from the game was the return of Alfie Potter, who was back in the squad three months after damaging ankle ligaments in the reverse fixture with Rovers.
Lewis was delighted to include the winger ahead of schedule, although it was always unlikely he would play after only returning to full training last Friday.
“Alfie put himself forward to go on the bench,” Lewis said.
“Ideally we didn’t want to use him, but he said he could do ten minutes if needed.”
- Highlights from the 1-1 draw, via Oxford United's Youtube channel