LONDON -- It took less than 20 minutes for the mask to slip.

After Ruben Semedo crept in behind Toby Alderweireld to score Olympiakos's second goal, Jose Mourinho turned to glare at the Tottenham Hotspur bench with a look that said, "Can you believe this?"

Then he was off, marching down the touchline, furiously clapping his hands together and animatedly urging his sleepwalking players to pick their heads up. Returning to his technical area, he ordered Tanguy Ndombele to warm up. In the 29th minute, he made his first change, sending on Christian Eriksen in place of Eric Dier. He cradled Dier's head briefly as the England international reached the touchline, and revealed afterward that he had apologised to the 25-year-old, but this felt like No More Mr. Nice Guy.

The night would end with Spurs' fans celebrating a 4-2 victory that swept last season's beaten finalists into the Champions League knockout phase for the third season running. But having been on a charm offensive ever since his appointment as the successor to Mauricio Pochettino last Wednesday, this was also the night when Mourinho showed his teeth for the first time.

If the two late goals that Spurs had conceded in last weekend's 3-2 victory at West Ham United had been easy to brush off -- footnotes buried beneath the joy and relief of a first Premier League away win in 10 months -- the first 45 minutes of Tuesday's Group B encounter at Tottenham Hotspur Stadium laid bare the depths of the malaise that the new manager must somehow attempt to dissipate.

Danny Rose, brought in for the injured Ben Davies in the only change to the starting XI that had taken to the field at London Stadium, could scarcely have done less to advance his case for a first-team place. The England left-back was at fault for both of Olympiakos' goals, gifting the ball to Youssef El Arabi for the visitors' sixth-minute opener and then falling asleep at the near post as Georgios Masouras' corner from the left was flicked on by Guilherme for Semedo to touch in the second.

Not that he was alone in fluffing his lines. Passes went astray at a rate that will have maddened Mourinho, who could at one point be seen urgently imploring Davinson Sanchez to calm down after the centre-back's crossfield pass toward Rose skidded off the turf for a throw-in. At that point, Olympiakos were everything that their opponents were not -- organised, energetic, tough in the tackle and slick in possession -- and with half-time approaching, their boisterous travelling fans would have been dreaming of a first Champions League victory in 13 attempts.

Had it not been for a calamitous mistake by Yassine Meriah in first-half stoppage time, they might yet have got there. As if afflicted by the contagion of sloppiness that seemed to be swirling around the stadium, the Tunisian centre-back completely miscued his attempt to clear Serge Aurier's low cross and Dele Alli accepted the gift to tap in his first Champions League goal since his match-winning brace against Real Madrid in November 2017.

In a reverse of September's 2-2 draw in Piraeus, this time it was Spurs' turn to come back from 2-0 down, and they duly equalised early in the second half when Aurier's quick throw-in -- abetted by a quick-thinking ball boy -- freed Lucas Moura, who scuttled to the byline before cutting the ball back for Harry Kane to level the score. There was a sense of inevitability about the four-minute salvo in which Spurs scored the two goals that carried them to victory, with Aurier slamming in a sweet half-volley after Alli's cross had been helped on by Son Heung-Min before Eriksen's free kick was headed in by Kane.

Mourinho wore a pensive look at full-time, biting his lip as the television cameras zoomed in on him as if to make it plain that were no grounds here for getting carried away. He had risked putting another player's nose out of joint 16 minutes into the second half when, with the score still 2-2, he had sent Moussa Sissoko on in place of Lucas. The Brazilian did not look best pleased.

Mourinho was at pains not to rebuke his players for their slipshod first half, explaining that many were still "tired" after their exertions during the international break, but if he is mindful that the problems that cost Pochettino his job will not evaporate overnight, he also made it clear that he will expect better against Bournemouth on Saturday.

"The next game at home, I expect the boys to start without ghosts," he said. "To start immediately open and confident to play. Because the players are very, very, very good players. So we have to play better than we did in the first half. We have to play better."

Having already shown signs of improvement in the final few matches of the Pochettino era, Alli has been a standout figure in both of Mourinho's first two games. The manager had spoken before the game of wanting to renew the "empathy" between players and fans, and there was a strong moment of solidarity when Alli made way for Ndombele in the 82nd minute, with the crowd standing to salute the 23-year-old midfielder as he slowly made his way around the perimeter of the pitch towards the bench.

Along with Aurier and the inevitable Kane and Son, Alli is emerging as a key man in the early stages of Mourinho's rebuilding job. But after this first show of power, there can be no doubting who is in charge.