The visitors took the lead early on when Alex Revell set up fellow striker Daniel Nardiello to nod in his fifth goal of the season from close range.
Sam Mantom's low volley levelled the game for Walsall after Rotherham failed to clear Andy Butler's corner, but 'keeper Scott Shearer will feel his could have done better.
Nardiello had a stonewall penalty appeal turned down after the break and new boy Tom Eaves had a header saved from Kari Arnason's long throw after a Matt Tubbs flick on, which was the closest either side came to a winner as the Millers kept up their impressive start to the season.