The Spurs forward opened the scoring in the north London derby but was sent off after just 18 minutes, and could only watch as his former club overran Andre Villas-Boas' side 5-2
The 28-year-old opened the scoring for the visitors after 10 minutes, but received his marching orders after a high challenge on Santi Cazorla which left referee Howard Webb with no option but to brandish a straight red.
And while the Spurs forward stressed his tackle was in no way malicious, he accepted his actions cost his side the victory - which leaves them 11 points off league-leaders Manchester City.
"I completely understand my sending off changed the entire outcome of the game and I whole-heartedly apologise to my team-mates, the manager and all the Tottenham fans for letting them down," he told The Sun.
"Nobody could have felt more devastated than me as I walked off the pitch.
"I so much wanted to help Tottenham win and thought for a moment that I'd actually set that win up when I scored, but football changes so quickly.
"One minute a hero, the next a villain."
However, the forward suggested while his tackle was foolish so early on in the game, it was an honest attempt to regain possession, with Cazorla being too quick for him.
He continued: "I must stress that my challenge was not malicious in any way whatsoever.
"I was genuinely trying to win the ball and probably stretched my foot out a bit too far in the heat of the moment."