Oxford United lost their first home game under Gary Rowett to Portsmouth following two second half goals.
Gary Rowett made just one change to the side that drew at Derby County on Tuesday, with Rúben Rodrigues returning to the side in place of Alex Matos.
Portsmouth had the first shot of the game after just 19 seconds and it came from former U's winger Josh Murphy, but he scuffed his shot and it was an easy take for Jamie Cumming. In the 10th minute Murphy was the creator as he floated over a cross that was met by Colby Bishop, his header going wide.
On 11 minutes the whole stadium, including Pompey fans and players, came together to applaud the memory of Joey Beauchamp.
This was followed almost immediately by the game coming to a halt for over half an hour as there was a medical incident at the back of the Family Area in the North Stand. The Club can confirm the person left the stadium breathing and is in a stable condition. We would like to take the time to thank everyone involved in dealing with the incident.
If Portsmouth had most of the possession before the stoppage, it was United that saw more of the ball after and looked more like breaking the deadlock.
There was a blow for the U's three minutes into the added time when Greg Leigh pulled up while chasing a pass and he had to be replaced by Sam Long, at playing left back. The half time whistle eventually blew one hour and 21 minutes after the game started.
The second half was just two minutes old when Portsmouth took the lead. United were unable to clear a Pompey corner and the ball eventually fell to Dozzell, just two yards out, and he had the easiest goal he's probably ever scored.
Oxford reacted well to the goal and had loud appeals for a penalty in the 52nd minute. These were waved away and this season's wait for a spot kick goes on.
Just two minutes after coming on, Ole Romeny's superb cross-field ball picked out the run of Płacheta whose first-time shot was expertly kept out by Nicolas Schmid for United's best chance so far. Romeny was involved shortly after with a cross across the area but no Oxford player was able to get on the end of it.
With time running out, Stan Mills managed to get on the end of a deep Tyler Goodrham cross, but he was unable to get his header on target. In the last minute of the 90, substitute Matt Phillips had a golden opportunity to equalise as he met Mills' superb cross but headed over from six yards.
In the end, all United's endeavours were in vain as in the final minute of stoppage time O'Mahony found himself with a free run on goal and he kept his composure to beat Cumming and seal the points for the visitors.
Oxford now have a week to lick their wounds, regroup and go again at the Hawthorns as they visit West Bromwich Albion next weekend.
UNITED: Cumming, Brown, Vaulks, Płacheta, Brannagan, Harris (Romeny 66), Rodrigues (Mills 66), Leigh (Long 45+8), Dembélé (Goodrham 66), Kioso (Phillips 83), Helik
Unused subs: Ingram, Phillips, El Mizouni, Matos, ter Avest
Attendance: 11,423 (including 1,479 away fans)
Fifty/50 draw: Ticket number 38278 wins £1.346
Report: Martin Brodetsky; Photography: JasonPix, Steve Daniels, Steve Edmunds, Darrell Fisher
