Heung-Min Son left League Two side Wycombe Wanderers heartbroken with a winner deep into stoppage time to send Tottenham through to the FA Cup fifth round by the skin of their teeth.

The eight-time cup winners appeared to be heading out as the battling underdogs went 2-0 up at the break and then 3-2 ahead in the 84th-minute. But Dele Alli levelled and Son won it after Mauricio Pochettino’s youngsters had failed to deliver.

Spurs made nine changes with only Kevin Wimmer and Eric Dier remaining as Georges-Kevin Nkoudou, Josh Onomah and Cameron Carter-Vickers were all drafted in.

Paul Hayes celebrates putting Wycombe ahead at White Hart Lane (Getty)

The trio failed to impress as the League Two side took the lead thanks to Paul Hayes’ double before Heung-Min Son and sub Vincent Janssen pulled it back. Garry Thompson then looked to have won it for Wycombe but in a thrilling finale, Tottenham turned it around again.

Much of the pre-match talk was over how the Premier League side’s players would handle the threat of 16 stone Wycombe forward Adebayo Akinfenwa and they certainly endured a tough afternoon.

Son's deflected shot brought Spurs back into the game (Getty)

The 34-year-old was instrumental in a move inside the first minute as he headed Sido Jombati’s cross across goal for Hayes to head against the crossbar.

Akinfenwa was then denied by Michel Vorm after heading at goal from Jamal Blackman’s free kick from his own goal. Tottenham were rattled but went close as Georges-Kevin Nkoudou closed in on goal only to be denied by a superb last-ditch Aaron Pierre tackle.

But it was Wycombe who belied their League Two status to create the better of the chances as Sam Wood volleyed over from Dominic Gape’s cross while the former saw a 35-yard lob just miss Vorm’s goal after beating the Dutchman.

The hosts still could have taken the lead as Heung-Min Son capitalised on a mix-up between Luke O’Nien and keeper Blackman but shot wide with the goal gaping.

Wycombe’s captain Hayes then saw an effort pushed away from distance but it was the underdogs who were to take a shock lead on 23 minutes.

Youngster Josh Onomah’s poor headed clearance from Joe Jacobson’s corner was met by Hayes with a sublime left-footed volley that had Vorm well beaten.

Vincent Janssen levelled the match from the penalty spot (Getty)

Hayes was to make a vital interception at the other end moments later as he cleared off the line to deny Moussa Sissoko who seemed destined to score.

It then take a brilliant Blackman save to keep out Son’s powerful drive and Pochettino’s side then appeared destined for an equaliser with a period of intense pressure.

Kieran Trippier’s volley from Ben Davies’ corner missed the target before another drive from Son just missed its target.

But Wycombe claimed a second thanks to Wood’s surging run on the break and when he was brought down by Cameron Carter-Vickers, referee Roger East had no option to point to the spot. Hayes produced a cool 36th-minute finish to beat Vorm and put Gareth Ainsworth’s side into dreamland.

Garry Thompson headed the visitors in front with just seven minutes of normal time remaining (Getty)

Wycombe could have made it 3-0 before the break as Akinfenwa’s header went just wide from Joe Jacobson’s cross and Pochettino did bring on Janssen at the break in a bid to turn things around.

But their frustrations continued at the start of the second half with Son twice missing the target from good positions but the South Korean got Tottenham back in the game with a deflected left footed strike on the hour.

Pochettino then made his final changes with Mousa Dembele and Dele Alli coming and Tottenham were to level on 64 minutes from the spot.

Aaron Pierre was adjudged to have blocked Janssen and the much-maligned Swede sent Blackman the wrong way.

Dele Alli's cool finish restored parity on the cusp of 90 minutes (Getty)

Wycombe went close to regaining the led within moments as Winks’ back header played in Wood who drove just wide.

But Tottenham had to play the last 17 minutes of the game with ten men after Trippier limped off with an apparent hip problem.

That looked to have cost them as Myles Weston broke down the left before crossing for Thompson to head home. But it was not enough for a shock as Alli burst through the Wycombe defence a minute from the end before another run from Son also breached a tired visiting defence.

“We gave absolutely everything. I thought we had it - twice,” said Wycombe manager Gareth Ainsworth. “It's taken their big boys to come on to make a difference. I'm so so proud. We had chances. Our goals were well-worked. We will absolutely pick ourselves up from this.”

Tottenham manager Pochettino hailed the performance of the League Two side. “Full credit to Wycombe they played very well,” he said. “Congratulations to them because they were heroes. We did not underestimate them. Credit them, we cannot play them down. It was very difficult for us. It was difficult to stop them, they showed more desire and quality on the pitch. It is only fair to say the truth.”

Tottenham Hotspur (4-3-3): Vorm; Trippier, Carter-Wickers, Wimmer (Dembele 61), Davies; Dier, Winks, Sissoko; Onomah (Alli 61), Son, Nkoudou (Janssen 46).

Subs not used: Walker, Wanyama, Lopez Sabata, Walker-Peters.

Wycombe Wanderers (4-3-3): Blackman; Jombati, Stewart, Pierre, Jacobson; Gape, O’Nien, Wood; Kashket (Saunders 77), Akinfenwa (Weston 68), Hayes (Thompson 77).

Subs: Richardson, Harriman, Bean, Saunders.