Match ends, Grimsby Town 1, Oxford United 3.
Teenage striker James Roberts marked his first start for Oxford with two goals as they cruised into round two of the FA Cup at blustery Blundell Park.
Lenell John-Lewis hit the post with a left-foot shot as Grimsby, unbeaten in seven games, made a bright start.
Roberts found the corner after cutting in from the left and tapped in another after Alfie Potter's shot was saved.
Danny Rose sealed the win when Grimsby failed to clear a cross before Shaun Pearson hooked in a late consolation.
A tight game looked on the cards in the first meeting between the two sides since 2005, with Oxford 19th in League Two and the Mariners second in the Conference.
The visitors, who reached the third round last season, went into the game without top scorer Danny Hylton, suspended after collecting five bookings, but had too much quality for Grimsby after Roberts had put them in front.
John-Lewis was booked for diving after going down in the box shortly after Rose's goal, but Pearson spoiled Oxford's hopes of a clean sheet after Jon-Paul Pittman's cross was headed down, his second goal of the season.
Grimsby boss Paul Hurst told BBC Radio Humberside:
"Disappointed to lose of course and get knocked out. Unfortunately, it was almost like we were nervous, a bit overawed and in the first half we weren't good enough.
"We didn't play the conditions either, but credit to Oxford.
"I just felt we didn't seem to get close to them, maybe dropped off a little bit deep. There were some things that were pointed out at half-time that I wasn't happy with.
"At two-nil it's difficult, but I still felt we had half a chance with the wind behind us - but the third goal killed it. Overall I have to say that Oxford were the better team. "
- 22NsialaBooked at 68mins
- 8DisleySubstituted forMcLaughlinat 59'minutes
- 20ArnoldSubstituted forNeilsonat 64'minutesBooked at 84mins
- 14John-LewisBooked at 53minsSubstituted forHannahat 70'minutes
- 25RileySubstituted forMeadesat 75'minutes
- 15O'DowdaSubstituted forBarnettat 85'minutes
- 31RobertsSubstituted forBrownat 85'minutes
- Chris Kavanagh
- Shots on Target
Second Half ends, Grimsby Town 1, Oxford United 3.
Foul by Ross Hannah (Grimsby Town).
Jake Wright (Oxford United) wins a free kick in the defensive half.
Foul by Jon-Paul Pittman (Grimsby Town).
Jake Wright (Oxford United) wins a free kick on the right wing.
Aristote Nsiala (Grimsby Town) wins a free kick in the attacking half.
Foul by Tyrone Barnett (Oxford United).
Substitution, Oxford United. Tyrone Barnett replaces Callum O'Dowda.
Substitution, Oxford United. Junior Brown replaces James Roberts.
Scott Neilson (Grimsby Town) is shown the yellow card.
Foul by Scott Neilson (Grimsby Town).
Danny Rose (Oxford United) wins a free kick in the attacking half.
Attempt saved. Callum O'Dowda (Oxford United) left footed shot from outside the box is saved in the bottom right corner.
Goal! Grimsby Town 1, Oxford United 3. Shaun Pearson (Grimsby Town) right footed shot from the centre of the box to the top left corner. Assisted by Craig Clay.
Jack Mackreth (Grimsby Town) wins a free kick in the defensive half.
Foul by Tareiq Holmes-Dennis (Oxford United).
Corner, Grimsby Town. Conceded by Tareiq Holmes-Dennis.
Substitution, Oxford United. Jonathan Meades replaces Joe Riley.
Foul by Patrick McLaughlin (Grimsby Town).