Record signing Andreas Makris scored his first Walsall goal but the Saddlers were pegged back by Oxford in an entertaining 1-1 draw.
Cyprus international Makris had not scored in 30 games since a summer move from Famagusta but lashed home from 20 yards, only for Chris Maguire's deflected strike to earn United a draw.
Walsall twice thought they had taken the lead inside the opening seven minutes but Scott Laird's tap-in was ruled offside and Kieron Morris rattled the post from 18 yards.
Morris also saw a 20-yard strike superbly saved by U's keeper Simon Eastwood later in the half.
Jon Whitney's Walsall took the lead after 47 minutes as Makris unleashed an opportunistic half-volley from 20 yards that dipped in off the bar.
Oxford almost levelled two minutes later as Walsall defender James O'Connor sliced Maguire's cross onto the post and Conor McAleny's follow-up was hooked off the line by Matt Preston.
United did level when Maguire's 25-yard strike took a wicked deflection in off O'Connor on 74 minutes and they almost won it as McAleny's 30-yarder was well saved by Neil Etheridge.