James Constable's brace coupled with Peter Leven's effort saw Oxford romp to a 3-0 npower League Two victory over Bristol Rovers, while United's bitter rivals Swindon were held to a 3-3 draw by Hereford.
Goals from Raffaele De Vita and Mehdi Kerrouche saw Paolo Di Canio's side go in at the break with a two-goal cushion, which was cancelled out after the interval by Tom Barkhuizen and Yoann Arquin.
Despite the setback, Swindon regained the lead through Simon Ferry but Harry Pell's last-gasp header earned a share of the spoils.
Plymouth's match with Accrington also ended in a high-scoring draw.
After Stanley saw Sean Hessey sent off, Simon Walton scored from the resulting penalty and Ladjie Soukouna extended their advantage in first-half stoppage time.
However, 10-man Accrington responded with gusto and, after Kevin Long pulled one back for the visitors, Padraig Amond ensured they would go back north with a point from the 2-2 draw.
Finally, Shrewsbury finished the right side of a five-goal thriller against Barnet at Greenhous Meadow.
The Shrews' two-goal half-time lead - courtesy of Matthew Richards and Terry Gornell efforts - was wiped out as Ricky Holmes and then Mark Marshall netted.
The latter's 82nd-minute goal looked to see the tie end as a draw, only for Lionel Ainsworth to score three minutes into stoppage time to secure a 3-2 win.
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