Sunday's clipping
Johnny's goal
Central defender Mullins drilled in a low 96th minute equaliser from just insider the box, but boss Chris Wilder admitted:
"There were a few gloomy faces in the dressing room, but I'm not down at all. It's a battling point. And it's a good start to the season with ten points from four games."
Dean Morgan put Wycombe ahead twice as Oxford dropped their first points of the season.
Former Oxford striker Morgan repaid the home crowd's jeers with a header from six yards in the 42nd minute.
Sunderland loanee midfielder Billy Knott nodded on a deep cross from central defender Gary Doherty and Morgan pounced to leave the defence flat-footed.
Dean's first goal
Morgan added his second from the spot in the 59th minute after he was up-ended by right back David Hunt.
And the second
But Wycombe had let Oxford back into the game in the 49th minute when defender Charles Dunne was shown a red card for lashing out at winger Alfie Potter.
The resulting floated free kick from midfielder Danny Rose on the right wing evaded everyone before bouncing into the net.
But Wycombe manager Gareth Ainsworth said:
"It was heartbreak, but only for a second. I feel huge pride and it was a great performance. It was something special after last week's home defeat."
On Dunne's sending off he added:
"We'll look at the DVD. If he did catch him in the face with an elbow, it was an accident in Charles's view. The biggest disappointment for me is to lose him now for three games."
As Oxford fought their way back into the game, keeper Matt Ingram pulled off two superb second half flying saves to shut out Dave Kitson and Mullins.
Wycombe deserved their lead and they had Oxford on the rack for most of the first half.
Morgan hooked one shot over from twelve yards and strike partner Stephen Craig saw a cheeky effort from the right flank skim over the bar.
And midfielder Nick Arnold's attempted lob on the stroke of half time needed to be clawed to safety by back-peddling keeper Ryan Clarke.
Morgan, 29, paid tribute to rookie boss Gareth Ainsworth who is still in his first year of management. He explained:
"He was once big enough to apologise for listening to some things other managers have said about me and I have total respect for him for that.
"Gaz already knows that you have to treat players as individuals and not just shout abuse at them which is what some managers have done to me in the past. I'll always give everything for someone who treats me with respect."
Meanwhile, Mullins has been dubbed 'the Magnet' by the rest of the squad. He revealed:
"The lads have nicknamed me 'the magnet' because it keeps falling to me in the box at the moment and long may it continue. I'd swap the goals for a clean sheet and a scruffy winner from someone else though.
"We're only four games into the season so we're not the finished article yet, but we're unbeaten."
My piece from the Monday edition