Cleveland's LeBron James, right, drives on Paul Pierce. Cleveland edged Boston, 88-77, on Monday in Cleveland.

Cleveland ? Back to even, and back to Boston – with authority.

LeBron James scored 21 points, jamming in a powerhouse dunk over a defenseless Kevin Garnett in the final two minutes, as the Cleveland Cavaliers beat the homesick Celtics, 88-77, in Game 4 on Monday night to tie the best-of-seven series at 2.

Still stuck in a shooting slump, James dominated down the stretch and finished with 13 assists – four in the fourth quarter. The Cavaliers, whose defense has been overlooked, held the Celtics to just 12 points in the final period.

“We took care of home court and turned it into a three-game series,” James said.

Boston dropped to 0-5 on the road in the postseason, a stunning slip for a team that went 31-10 on the road during the regular season.

“It’s hard to say. I have no answer for it,” Boston guard Ray Allen said.

During a short visit to Ohio, the Celtics lost their momentum in the series, but now will head home, where they went 35-6 before the playoffs started.

Game 5 is Wednesday night, and Game 6 will be back in Cleveland on Friday.

“We’re disappointed right now,” forward Paul Pierce said. “I had a lot of shots that I usually make, but I’m not going to really dwell on it.”

James was just 7-for-20 from the floor, but he did everything else for the Cavs, who are attempting to overcome an 0-2 deficit for the second time in two years.

In the final 8:45, James had four assists, a three-pointer and a right-handed dunk that rattled Quicken Loans Arena and became the signature moment of this series.

With the Cavs leading, 82-75, James drove past Pierce on a screen near the foul line, head-faked past James Posey, and then posterized Garnett, the league’s defensive player of the year. As Cavaliers fans erupted, a scowling James stormed back on defense.

“I just wanted to be aggressive. I hadn’t had a play like that all series,” James said.

Daniel Gibson and Wally Szczerbiak added 14 points apiece, and Anderson Varejao had 12 and made two jumpers in the final 1:10 to put the Celtics away.