The young striker had only been on the pitch seven minutes when he rose unmarked to head in a free kick from Chris Hackett.
And it salvaged a draw from a pulsating local derby which Oxford must have thought they had thrown away.
The were on top for the first half and took the lead through Hackett's first ever goal at the Kassam Stadium.
The right-winger arrived at the far post to finish off a four-man move by getting on the end of a Craig Davies cross.
Oxford had been first to the ball and closed down very well, Wycombe looked a different side when they attacked with menace.
Manager John Gorman sent on Ian Stonebridge and Stefan Oakes just after the hour and they made a difference.
On the 69th minute Nathan Tyson equalised with an angled shot after goalkeeper Billy Turley saved from Roger Johnson.
The move had been engineered by Kevin Betsy, who broke down the right and it was Betsy who created a second goal for Tyson after 85 minutes with more great play down the right. He carved open the Oxford defence and Tyson converted his cross with a shot into the roof of the net.
But Morgan capitalised on poor marking by burying his free header passed Frank Talia to make it 2-2.