There was no late drama in the Eastern Conference, where the
Although the 76ers lost by a bigger margin, it will be the Lakers who will probably be suffering more due to the manner of their loss.
Kobe Bryant and Andrew Bynum both scored 20 points as the Lakers led 75-68 with two minutes left and looked set to inflict a first defeat on the Thunder in the playoffs this year.
But Oklahoma then rallied with James Harden scoring four in those final minutes and Kevin Durrant five, including a soft floater to put the Thunder ahead with 18 seconds remaining, to leave the home fans ecstatic.
"We kept our composure," Durant told reporters after scoring a team-high 22 points. "We've been growing as a group at the end of games. This is the playoffs, every possession is important."
The Lakers had a chance to win the game but Steve Blake misfired on an open three-pointer with Los Angeles trailing by one with three seconds on the clock. Durant then landed a final free throw to add to the Lakers' pain.
It was one of a number of mistakes made by the experienced Los Angeles side late on. Two consecutive turnovers in the final minutes soured a credible defensive effort that saw them contain the lively Thunder.
Oklahoma City had crushed the Lakers by 29 in the opening game but Los Angeles were able to control the pace and the contest until the final, fatal minutes.
The Lakers will need to lift themselves for Game Three in Los Angeles on Friday.
In the East, the evergreen Kevin Garnett pushed his 35-year-old body to contribute 27 points and 13 rebounds, while Paul Pierce and Rajon Rondo also added double-doubles for the Celtics.
The 76ers ignited the home crowd by taking a 33-28 lead after the first quarter, but the Celtics flipped a switch in the second and never looked back.
Fired by Garnett and a stout defence, the visitors held Philadelphia to just 33 points over the second and third quarters to carry a 23-point lead into the fourth.
"We were fuelled by defence," Garnett said. "I thought we got turnovers and stops and it gave us offence."
Thaddeus Young finished with 22 points to lead the 76ers, who will look to rebound at home in Game Four on Friday.
Pierce collected 24 points and 12 rebounds for Boston, with Rondo scoring 23 and contributing 14 assists.