Cleveland, OH (AP)  -- 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 2-2.

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.

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. During a short visit to Ohio, the Celtics lost their momentum in the series but will now 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.

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 3-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 Paul 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.

Although James is shooting only 20-of-78 (26 percent) from the floor, the only numbers the Cavs care about are the pair of 2s that show this series is as tight as possible.

Garnett scored 15 points, but only two in the second half, as Cavs forward Anderson Varejao harassed Boston's All-Star all night. Ray Allen had 15 points and Paul Pierce 13, but the Celtics' Big Three were only a combined 16-of-40.