Matt Ritchie gave the hosts the lead in the eighth minute only for midfielder Danny Hollands' to put through his own net two minutes later.
Doncaster were twice rescued by the woodwork before the half-time whistle and an honest Saunders admitted: "We got battered at times.
"But we dug in to get a draw when we were nowhere near our best.
"Swindon got lots and lots of balls into our box but we defended well and our goalkeeper had the most to do all season, and the woodwork helped us as well.
"We are still second and a point away at Swindon is good. Swindon will be in the top six at the end of the season but the main thing is they didn't beat us.
"Swindon were favourites to go up before the season started and we wasted opportunities early in the game as a few of us struggled, but we pulled through."