DALLAS — The Dallas Mavericks still can’t stop Phoenix’s inside-and-outside playoff combination, even with Amare Stoudemire on the bench with an injury this year.

Boris Diaw took over Stoudemire’s starring role from last postseason, scoring 34 points — including a turnaround 7-footer with 0.5 seconds left — to cap a tremendous closing finish, sending the Suns past the Mavs 121-118 Wednesday night in a thrilling, fast-paced start to the Western Conference finals.

Steve Nash remained the outside force, scoring 27 points and adding 16 assists, the most by anyone this postseason and one shy of his career playoff high.

Devin Harris scored a career-high 30 points for Dallas and Dirk Nowitzki had 26 points and 19 rebounds for the Mavs, who host Game 2 on Friday night.

The Mavs seemed in control, leading 114-105 with 3:43 left, when Nash began playing like the league’s two-time MVP. He scored 10 straight points, then fed Shawn Marion on a go-ahead dunk with 43 seconds left.

Harris put Dallas back ahead with a 16-foot jumper with 4.8 seconds left. But after a timeout, Diaw took the inbounds pass, pump-faked defender Jerry Stackhouse, then spun and swished the winning basket from the right side of the lane.

“Coach called the play,” Diaw said. “Steve Nash was supposed to (go) backdoor. It wasn’t open. With seconds going down, I shot it.”

Dallas had a throw-in from near the Phoenix bench, but Marquis Daniels got his signals crossed with Dirk Nowitzki and threw it out of bounds. The Suns tacked on two more points with 0.2 left on a pair of free throws by Tim Thomas.

Officials took several minutes to decide how much time remained when Thomas was fouled. With fans streaming out, Nowitzki threw the ball at the front of the scorers table in anger. After the shots, he threw the final inbounds pass to the other foul line, where Diaw tipped it away, capping Phoenix’s opening salvo that snatches home-court advantage.

In the second round of last year’s playoffs, the Suns beat the Mavericks in six games, with Stoudemire and Nash doing most of the damage.

The big man scored between 30 and 40 each of the first three games, then the Mavericks began focusing on him and Nash burned them with between 34 and 48 over the last three games.

Although both teams were coming off Game 7 wins Monday night, there was no emotional or physical letdown either way.

It was 62-58 at halftime and both teams were making at least half their shots. They were even more accurate in the third quarter, surpassing the Game 1 scoring total from the Eastern Conference final between Miami and Detroit before the fourth even began.

The Suns led for the first 21/2 quarters. After Harris led Dallas on a 13-2 go-ahead run, Phoenix came right back.

The Mavericks followed with a 13-0 run spanning the end of the third and start of the fourth that seemed to have them in control. When the Suns got within 106-103, Dallas opened the lead again.

Both teams saw starters leave with leg injuries. Dallas’ Josh Howard sprained his right ankle midway through the first quarter and will have an MRI Thursday to see about a possible return.

Phoenix’s Raja Bell strained his left calf midway through the fourth quarter and didn’t return.

Diaw, an undersized center at 6-foot-8, showed why he was voted the league’s most improved player, hitting 13 of 23 shots, including the most important one.

Marion had 24 points and 13 rebounds, and Tim Thomas scored 17.

Stackhouse scored 16 points and Jason Terry added 15. Daniels had nine and Keith Van Horn, who is likely to see a lot of time this series, scored seven on 3-of-11 shooting. He was 1-of-7 on 3-pointers.

Harris, who had only nine points the two previous games, made eight straight shots in the second half and finished 12-of-17.

Dallas came out in no hurry to shoot, taking as much time off the clock as possible on every possession. Phoenix foiled that strategy by seemingly getting to the other end faster than ever, either scoring ahead of the defense or with a secondary wave of players after the first few Mavs caught up.

Nash was more instigator than scorer, with five assists and only three shots (and three points) in the opening period.

Things changed in the second quarter, with the Mavericks running and Nash shooting.

He scored six of seven Phoenix baskets in one stretch, mixing left-handed layups, fadeaways and outside jumpers. Thomas had the lone other basket, flying past Nowitzki for a tremendous dunk.

Playoff Notes

Trying to save a loose ball in the third quarter, Leandro Barbosa instead spiked it hard into assistant coach Marc Iavaroni. ... Dallas C Erick Dampier started for the second straight time after having coming off the bench since January. Deposed starter DeSagana Diop, who broke his nose Monday night, didn’t play.