The Rockies were a strike away from victory in Thursday’s matinee at Chase Field but folded instead when closer Pierce Johnson blew his first save of the year to send the Diamondbacks to a 5-4 walk-off win.

Rookie outfielder Corbin Carroll delivered the two-RBI single in the ninth off Johnson that gave Arizona its first fourgame sweep over Colorado in 21 years and sunk the Rockies further into the basement of the National League West.

Arizona, meanwhile, moved into a tie with the Dodgers for first place in the division with the comeback victory that erased a strong outing from Colorado right-hander Connor Seabold and the would-be winning homer from rookie shortstop Ezequiel Tovar.

Seabold threw 5 1/3 innings and was tagged for one earned run, with five strikeouts to two walks. But the bullpen leaked oil into the ninth before Johnson (11-of-11 on save chances coming in) gave away the game.

“(Johnson) is not invincible,” Rockies manager Bud Black told reporters. “His stuff was good, and he was fresh. Carroll got a fastball that wasn’t located quite high enough in the zone, and he poked it into left field.”

Brenton Doyle got Colorado on the board first with his two-out single to score Mike Moustakas and make it 1-0. But the offense went quiet after that as Seabold cruised through five innings with no runs and just three hits allowed. He kept Arizona off balance with a healthy mix of changeups (19) and sliders (13) to go along with 59 fastballs.

“That was the most complete my repertoire has been since spring training,” Seabold told reporters.

Colorado finally got more breathing room in the sixth against D-backs righthander Zach Davies. The red-hot Ryan McMahon, hitting .500 in his prior seven games coming into Thursday, led off with a double. Harold Castro singled him home, then Nolan Jones singled home Castro a couple batters later off southpaw reliever Kyle Nelson.

The Rockies had a 3-0 lead, but it wasn’t safe. After Seabold walked Starling Marte to open the bottom of the sixth, he got an out and then got the hook from manager Bud Black.

“It looked like (Seabold) was wobbling a little bit,” Black said.

Right-hander Jake Bird came on and promptly gave up a single to Christian Walker and a two-RBI double to Yuli Gurriel, cutting the visitors’ lead to 3-2. But Bird got out of trouble with a couple of K’s.

In the seventh, Tovar lead off with a 413foot blast to center off Nelson that showed off the rookie’s raw power. The dinger continued the recent offensive surge for Tovar, who was hitting .314 with a couple homers in the 15 games before Thursday.

But again, Arizona came right back in the bottom of the inning, dinging Brad Hand for a run via Marte’s RBI double to make it 4-3.

Justin Lawrence got the final out of that inning and then tossed a scoreless eighth to set up Pierce Johnson for the save in the ninth. But Johnson couldn’t close the door. A one-out walk to Gabriel Moreno, followed by Marte’s two-out double, set up Carroll’s game-winning knock.