Daniel Farke's side had been the more forceful team after the interval and were rewarded when Harry Wilson's pass found Okafor, who drove a low finish past Antonin Kinsky. Okafor scored 97 seconds after coming on.
Farke was delighted with the response from his players, saying: "We were pushing to win this game and were relentless. We showed great spirit, commitment and unity. It was a fully deserved win."
The Leeds United manager was asked about the flashpoint involving Jayden Bogle and Mathys Tel. Bogle's challenge left the Tottenham forward injured, but the Leeds defender escaped a red card following a VAR review.
"I haven't watched it back. I have heard there were several doubtful situations. A possible hand ball. I just know that Jayden Bogle out of any bad intention. It looked like a coming together.
"It's very unlucky outcome that Mathys is injured and we wish him all the best and he can recover quickly. The last thing Jayden Bogle is a nasty player. He's possibly the softest player in the whole league. I always call him my butterfly, and I can guarantee it was never out of bad intention."
De Zerbi, meanwhile, did not attempt to disguise his frustration with Tottenham's display after the break.
"We deserved to lose the game in the second half and didn't play like we can. It's a journey for us, because we can learn from this game. I am sorry for the performance in the second half - we didn't play like a top team. We didn't have the right character and physicality in the second half."
The Italian questioned the booking shown to Pedro Porro, comparing it with Bogle's challenge on Tel.
"Pedro Porro's was a duel and an incredible yellow card. The first situation of Mathys Tel I didn't see, I can't say nothing."
Asked whether the referee should have been sent to the pitchside monitor, De Zerbi replied: "No. I have big confidence in the referee. Nothing changes if he goes to the monitor. If they didn't take the right decision I don't know. We have to keep the eyes on the performance where can improve."
Leeds held on to secure three important points, while Tottenham were left to reflect on a second half that their head coach felt fell well below the level expected of his team.