Relegation-threatened Walsall sacked manager Dean Keates after 10-man Oxford virtually ensured their League One safety with victory at the Banks's Stadium.
Oxford had to play the entire second half a man light after Marcus Browne's red card but still recorded a fourth win on the spin to finish the day in the top half of the table.
The Yellows led on 20 minutes when Everton loanee Luke Garbutt's free-kick was headed home by an unmarked Rob Dickie.
Walsall levelled on 26 minutes as Andy Cook robbed United defender Curtis Nelson to prod home his 17th goal of the season before Oxford were reduced to 10 men when Browne was given a straight red card for a studs-up challenge on Zeli Ismail in first-half stoppage time.
But they regained the lead on 63 minutes as Garbutt was allowed space to fire home Sam Long's low cross.
Jon Guthrie headed a golden chance for a Walsall equaliser wide and Jerome Sinclair sealed the points with a cool stoppage-time finish.
United's Ahmed Kashi, who had earlier been booked and then substituted, was shown a second yellow for coming on to the field to celebrate the goal.
A Walsall statement after the game read: "Walsall Football Club have tonight parted company with manager Dean Keates with immediate effect."
Match report supplied by the Press Association.
