Andre Villas-Boas denied complacency got the better of his Tottenham team after they threw away a lead to leave Panathinaikos with a point.
Spurs were in complete control of their Group J game against the Greek side and took the lead after 35 minutes when Michael Dawson glanced Tom Huddlestone's cross past Orestis Karnezis.
Jermain Defoe, Gareth Bale, Clint Dempsey and Huddlestone then all missed chances to put the game to bed and Panathinaikos took full advantage through striker Toche, who left Dawson for dead and turned in a Giorgos Seitaridis 13 minutes from time.
Panathinaikos, who sit 12th in the Greek Super League after a dismal start to their season, lacked any penetration until the latter stages of the second half and were there for the taking.
Villas-Boas, whose team now sit third in Group J, two points behind Lazio, brushed aside suggestions his team thought the game was over before the final whistle.
"I don't think we were complacent," Villas-Boas said.
"We have to give credit to Panathinaikos, they pressed much more and started to gain belief from that and that led to the goal.
"I think the whole team felt a bit disappointed because the first half was so positive and we were in control of situation.
"We were a bit sloppy in the second half. I understand the disappointment at not putting the game to bed, but in the end we congratulated the players because if it had been other way round, the whole perspective would have been different.
"Panathinaikos came at us very strong in the second half, they made a change with Ibrahim Sissoko. He improved the quality of their game and could not stay in control of game so much in second half."
Dawson has found first-team opportunities hard to come by since Villas-Boas arrived at the club despite his status as club captain.
The 28-year-old, who turned down a £9million move to QPR this summer, is effectively fifth-choice centre-half and only started the game because Villas-Boas rested William Gallas.
Dawson's lack of match sharpness was evident in the first half when he was out-paced by Toche and Lazaros Christodoulopoulos and he almost put the ball in to his own net after the break.
With Lazio beating Maribor in the night's other game, Spurs may find it hard to qualify if they fail to beat the Slovenians in their next game, but Villas-Boas is not panicking.
"In the end it leaves us with two points. Maribor have three and Lazio have four so everything is open as we go into the double-headers," Villas-Boas said.
"It's only after the fourth game that you tend to know who will go through or whether there is any competition for that second place.
"In a group like this, normally 10 or 11 points to qualify."
Villas-Boas won the competition with FC Porto two years ago and tonight re-iterated his desire to lift the trophy again with his new club.
"The ambition we set for this competition is to go to the final, to win the trophy," the 34-year-old said.
"It is a trophy this club have won in the past so we embrace this tradition. We will try to qualify from this group and then take it from there."