Tottenham pulled ahead just before the 20-minute mark. Copenhagen clumsily gave the ball away in the Spurs half, allowing Rodrigo Bentancur to win possession back and hand the reins over to Xavi Simons, who quickly saw Johnson darting in behind the high defensive line and fed him down the right-hand channel. Goalkeeper Dominik Kotarski came a long way out of his box to challenge Johnson and missed, with the Welshman cooly rolling the ball in from a tight angle.
Spurs ought to have doubled their lead before the break when a lovely, flowing team move saw Simons square the final pass for Randal Kolo Muani, who somehow fumbled the chance to score his first goal for his new club by firing wide from close range.
Shortly after the restart, the hosts found that second goal. Pedro Porro's long ball over the top was chased all the way by Kolo Muani, who blocked Kotarski's clearance and retrieved the high clearance with an immaculate first touch before selflessly passing to Wilson Odobert to finish.
But the game threatened to turn when Johnson was shown a red card on 57 minutes. The winger caught Marcos Lopez on his heel with his studs, and after consulting with VAR, the referee gave him his marching orders.
However, that only seemed to galvanise Tottenham, who scored their third of the evening soon after. Joao Palhinha nicked the ball back on the edge of the Spurs penalty area, and Micky van de Ven proceeded to sprint almost the entire length of the pitch before firing beyond a helpless Kotarski. Seconds later, it was four as another quick breakaway saw Odobert slip in centre-back Cristian Romero, who managed to reverse the ball back for Palhinha to smash in at the back stick.
Richarlison rattled the underside of the crossbar with a powerful header from a Porro cross before Spurs were awarded a penalty when Dane Scarlett was tripped by Junnosuke Suzuki. Brazil's No.9 stepped up and, would you believe it, hit the exact same spot on the bar again. However, that mattered little in the grand scheme of things as Tottenham ran out convincing winners.
GOAL rates Spurs' players from Tottenham Hotspur Stadium...
Guglielmo Vicario (6/10):
Once roundly criticised for his inability to catch a cross, the Italian goalkeeper guarded his six-yard box superbly to hoover up Copenhagen crosses. Only really tested by way of shot-stopping from distance.
Pedro Porro (7/10):
Gave the ball away a couple of times in his own half early doors but was much better defensively here than he has been all season. Came up with the daring long ball which led to Odobert's goal.
Cristian Romero (7/10):
Swept up for Van de Ven whenever the Dutchman went marauding into midfield in a role-reversal of their usual tasks. Found himself playing up front for a brief few seconds before teeing up Palhinha for Spurs' fourth goal. Subbed for Danso.
Micky van de Ven (8/10):
Wow. Came into the game with a point to prove after walking off without clapping the fans against Chelsea on Saturday, left as the name on everyone's lips for the right reasons. Hardly troubled at the back and then ran Copenhagen ragged with one hell of a sprint right through their entire team to score Spurs' third.
Destiny Udogie (7/10):
Spurs have missed natural width down the left despite the emergence of Spence as an outstanding one-v-one defender. Combined well with Odobert throughout. Taken off for the England full-back eventually.