Leeds certainly had the greater share of the chances in the first half but after Gus Poyet's stunning opener, O'Leary had to rely on two errors for the goals that maintained his side's lead in the Premiership.
"We dominated the game and I was very disappointed at half-time that we weren't a couple of goals up," said O'Leary.
"They scored a very good goal with what was really their first chance even though I thought it was a soft goal from our point of view. I'm sure Glenn is saying they gave away two soft goals as well.
"I thought we were always the dominant team. I was delighted with the players because they were tired and we didn't get back from France until Friday morning. That makes you vulnerable.
"It was a good three points against a team who has been on a good run and a team that, individually, have players who can do what Poyet did today."
David O'Leary said he believed that the best side won Sunday's encounter at Elland Road.