Ross Stewart looked to have secured the points with a 92nd minute goal, his second in what was another superb attacking performance from the Scot.
Sunderland had dominated the second half and created the better of the chances throughout, but the home side’s relentless set piece paid off with what was virtually the last kick of the game.
A serious injury to Corry Evans served as another blow to an already depleted squad.
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What would already have been one of the toughest challenges of the season for Sunderland had been made even more daunting by the absence of seven players due to COVID-19, with injuries taking the tally of absentees well into double figures.
Only the recall of three loanees had taken Johnson’s side to the total required to fulfil the fixture, and for Anthony Patterson it would be a start against one of the most physically imposing sides in the division.
It made the opener all the more striking, a superb goal just three minutes into the contest.
Embleton, Winchester and Stewart combined to work the ball out to the left flank, and the latter broke late into the box to meet Dennis Cirkin’s precise cross with a thumping header. The ball struck the crossbar, but hit David Stockdale and rolled into the net.
Wycombe quickly regained their composure, beginning to play the way that has brought them so much success over recent years. Dangerous set plays, picking up second balls in the wide areas.
Only a superb save from Patterson denied Ainsworth’s side an instant response, the young goalkeeper showing his impressive reflexes to deny Vokes at close range after a good low cross from the left flank.
The lead would last a matter of minutes all the same. Flanagan did superbly to make two blocks inside the box but the visitors were unable to clear their lines and that allowed Mehmeti to shoot from the edge of the area. It was cleanly struck, but Patterson looked to have it lined up before a deflection took it past his outstretched hand.
The Black Cats did look a threat when they were able to get into the final third, with Stewart’s off-ball excellence particularly notable.
But the ball retention was not quite good enough, giving the hosts too many chances to fire the ball into the final third from deep.
Ten minutes from the interval the pressure finally told, Stewart unable to clear a corner at the back post. The ball hung under the bar and though Hanlan appeared to be impeding Patterson from an offside position, no foul was given and Vokes was able to nod home from little more than a yard out.
Sunderland had looked lively on the counter at times, but after that fast start the game looked to be drifting away from them a touch.
Wycombe looked comfortable, but were pegged back within minutes and it was another outstanding Sunderland goal. Embleton stood his marker up on the left, beating him on the outside and driving a wicked low cross to the front post. Stewart got across his marker and did superbly, a deft first-time volley leaving Stockdale with no chance.
After a pulsating first half it was honours even at the break.
Johnson’s side started the second with a superb move that sliced the home defence open, but Stockdale did well to rush off his line and deny Corry Evans.
It would have been a fine assist for Pritchard, who followed it up with another two superb through balls that Embleton and then Gooch just weren’t able to gather in time.
They went even closer when Stockdale spilled a long-range shot from Pritchard, Jacobson making an outstanding clearance to deny Stewart’s headed follow up.
While Wycombe did threaten sporadically, it was Sunderland who continued to look the most threatening and they were inches away from a deserved lead when Embleton drove through the middle of the pitch and struck the crossbar with a superb long-range effort that had Stockdale beaten.
The concern was that they hadn’t been able to make the most of their threat, and that was underlined when Grimmer raced onto a second ball and fired into the side netting.
Sunderland twice went close through Winchester, but either side of his efforts there was major concern for Evans, taken off on a stretcher after a collision with his own goalkeeper. It had been excellent from Patterson, racing off his line to head a long ball clear, but the severity of the injury was immediately clear and led to a long delay.
The Black Cats continued to press even despite that loss of momentum, but it looked as if the win might prove elusive when Stewart turned an excellent cross from Gooch just over the bar from inside the six-yard.
Nine minutes of stoppage time offered hope, though, and within two minutes of it the away end would explode.
Neil did well to win a loose ball and released Gooch, who slid a through ball for Stewart. The defender looked to have the advantage, but the striker galloped past him and turned his effort past the onrushing Stockdale.
Sunderland were moments from taking the three points when Wycombe slung the corner in, Jacobson rescuing the draw from close range.
Sunderland XI: Patterson; Winchester, Flanagan, Doyle, Cirkin; Evans (Diamond, 79), Neil; Embleton, Pritchard, Gooch; Stewart
Subs: Carney, Younger, Hawkes, Xhemajli, Hume (D), Taylor
Wycombe Wanderers XI: Stockdale, Grimmer, Jacobson, Stewart, Vokes (Akinfenwa, 88), McCleary, Hanlan, Mehmeti, Scowen, Obita, Forino
Subs: Pryzbek, Tafazolli, Thompson, Horgan, De Barr, Pendlebury
Bookings: Scowen, 21 Jacobson, 45 Embleton, 82