Two down, two to go.
But now comes the real test as the series shifts west for the next three games.
When they visit the Los Angeles Lakers in Tuesday night's Game 3, the Celtics will attempt to do something no team has managed to do this postseason: win at Staples Center.
In the first three rounds of the playoffs, the Lakers are 8-0 at home. Counting the end of the regular season, the Lakers have won 14 straight at home, with their last defeat coming March 28 to Memphis.
Homecourt advantage has been key during this postseason, with home teams combining to go 61-21 thus far. Twelve of the 14 teams holding homecourt advantage have advanced to the next round, with Utah's victory over Houston and San Antonio's win over New Orleans the only exceptions.
So opening the finals with a 2-0 record comes as no surprise to the Celtics.
"We've done what we should do," Celtics coach Doc Rivers said. "We took care of home, and that's what we should have done. Now we have to go on the road for us to keep attacking."
Rivers and his players are well aware the Lakers have plenty of fight left. That was evident in the fourth quarter of Game 2.
Boston rebounded from a first-half deficit to go up by 24 points in the third quarter. But the Lakers persisted and reeled off a sizzling 41-point fourth quarter fueled by a 7-for-11 shooting performance from 3-point range.
Los Angeles pulled within 104-102 with 38 seconds remaining but ran out of time and fell 108-102.
"Definitely a lesson to be learned in that last six minutes," said Celtics forward Paul Pierce, who led his team with 28 points. "Just down the stretch, we've got to be a little more aggressive."
Aggression will prove critical for the Celtics, who until winning two games in Detroit during the Eastern Conference finals had lost six straight road playoff games.
The Lakers, meanwhile, hope they have finally gotten past the lack of offensive rhythm and physical play that resulted in only 88 points in Game 1 of the finals. The same disjointed play caused them to struggle for three quarters before they finally hit their stride in the fourth quarter of Game 2.
"I'm not worried about which Celtics team shows up," Los Angeles coach Phil Jackson said. "I'm worried about what Lakers team shows up. That's the one that moves the ball and we do things well on the offensive end, and you saw that as the game progressed that we started finding our rhythm on the offense."
Increased production from center Pau Gasol and forward Lamar Odom will help the Lakers' cause. Both players have been inconsistent in the finals. Gasol went the entire first half of Game 1 without a rebound, and in Game 2, after leading his team with 13 first-half points, the Spaniard scored only four points in the second half.
Odom scored only two points in the second half of Sunday's loss, and his inability to read the Celtics' defensive schemes is hurting his team.
"Lamar got confused out there tonight, and that was difficult for him," Jackson said after Sunday's game. "Situations that got him into foul trouble and little offensive sequences that rather than just taking a shot or making the right play looked like he was a confused player out there at times. We'll try and get that straightened out."
Aware that the Celtics will be focusing on getting off to a quicker start and maintaining their aggression throughout the game, the Lakers realize they need to match that tone. Their hope is that they can duplicate the latter portion of Game 2's effort in Game 3.
"We played with a sense of desperation and more aggression," Lakers guard Kobe Bryant said. "And I think that's something for us to take home and learn from."