Toronto needed a run in the ninth and two in the 10th to stave off the Orioles, who led 2-1 going into the bottom off the ninth and then went ahead 3-2 in the 10th thanks to Dariel Alvarez's solo homer off reliever Arik Sikula.
Toronto pinch-hitter Erik Kratz doubled with one out in the 10th and moved to third on a wild pitch. Diaz walked and Dan Johnson singled in Kratz to tie it at 3-3. Josh Thole, who was three-for-17 at the plate, then grounded out to Buck Britton at second base but Diaz beat the throw to home from first baseman Michael Almanzar.
Diaz said third base coach Luis Perez deserved kudos for the play
"It was 3-1 (count) and we were just going on the pitch," said Diaz, a slick-fielding shortstop who had come on earlier as an outfield replacement. "I give all the credit to Luis. He's the one that saw the play and sent me.
"And I just put my head down and ran as hard as I could. Luckily I was the winning run. That's exciting."
The win snapped a four-game spring losing streak for the Jays (7-10), who had looked poised to end that slide in the ninth inning.
Toronto outhit Baltimore 15-10 in a game that started slow but ramped up at the end. While hardly a classic — the two teams combined to leave 20 men for base — it had its moments.
The game, played on a 26-degree day at Florida Auto Exchange Stadium with a stiff wind blowing in from right field, drew a crowd of 4,605.
Sikula, a 23-year-old minor-leaguer, ended up with the win after looking like he was going to take the loss.
Toronto sent it to extra innings with a run in the ninth after loading the bases with no outs off reliever Ryan Webb through singles from Johnson, Dioner Navarro and Chris Getz. Munenori Kawasaki then hit an RBI single to tie it at 2-2.
But the promising rally ended all too quickly.
Baltimore (10-6) brought in left-hander Kelvin De La Cruz, who retired Moises Sierra via a sharp lineout. Kevin Pillar then hit a double-play ball back to the pitcher to end the uprising. And the Orioles made the Jays pay — at least briefly — in the 10th with the homer.
De La Cruz took the loss while Webb was tagged with a blown save.
The Orioles went ahead 2-0 in the fourth on RBI doubles by Steve Clevenger and Ryan Flaherty after Adam Jones got on board on an infield hit and moved to second on a Todd Redmond wild pitch.
Toronto pulled one back in the bottom of the fourth.
On the plus side, the Jays continued to display good defence with Brett Lawrie handling hot shots at third in the second and fourth innings and Colby Rasmus tracking down a high ball in the wind in the third. Melky Cabrera gunned down Almanzar from left field in the seventh as he tried to come home from second on a single.
Chunky catcher Navarro, however, was thrown out at the plate to snuff out a Jays rally in the seventh.
Redmond, the Jays starter, scattered four hits over five innings, giving up two runs. He struck out four and walked one.
He gave way to 2010 first-round draft choice Aaron Sanchez, whose fastball hit 97 m.p.h. on the speed gun during a Houdini-like appearance that saw the 21-year-old live dangerously but somehow survive.
Sanchez loaded the bases with no outs in the sixth but escaped with a double play that removed the lead runner and a groundout. In the seventh, he kept the Orioles from scoring after putting two men on base.
Redmond came into the game having given up seven earned runs and 11 hits in four spring outings for an ERA of 7.00. The 28-year-old right-hander is out of options, meaning another club could pick him up if the Jays sent his down.
Redmond had 1-2-3 innings in the first, third and fifth but had traffic on the bases in the second and fourth.
"My last two outings (have been) definitely in the right direction," said Redmond, hoping to stick with the big league team.
Orioles starter Miguel Gonzalez, who went 11-8 last season with a 3.78 ERA, retired 10 straight between first and fourth inning before running into some trouble. He exited after four innings, yielding one run on five hits with three strikeouts.
Singles by Edwin Encarnacion, Adam Lind and Cabrera with two outs in the fourth produced a Jays run, with Jones' throw from centre making it close at the plate. Lawrie made it four singles in a row to load the bases but the five-foot-nine 205-pound Navarro grounded out to end the rally.
The Jays looked to do it again with two singles in the fifth against reliever Alfredo Aceves but second baseman Jemile Weeks snuffed out the charge with an acrobatic catch of an Encarnacion broken bat hit.
The Jays have an off-day Monday before travelling to Lakeland to face a Detroit Tigers split squad on Tuesday. Ricky Romero is slated to start in his continued bid to win back a place in the Jays' rotation.