The Toronto Blue Jays starter had just delivered the seventh pitch of the game when he felt a pain in his side. After two more throws, he was done.
Morrow lasted just nine pitches after straining his left oblique muscle on Monday as the Washington Nationals defeated Toronto 6-3 in the opener of a three-game interleague series.
Morrow left in discomfort while facing a 2-1 count against Nationals rookie sensation Bryce Harper in the first, walking to the clubhouse unassisted after being checked out by trainers and manager John Farrell.
"I felt it on the first pitch to Harper," said Morrow, who was tagged with the loss. "I felt like a stabbing in my side when I threw it. I just put it out of my mind for the second pitch, just threw it like nothing happened, hoping it was nothing. Threw (the next) one and felt the same thing.
"Then of course I was thinking about it on the third pitch and wasn't able to deliver the ball very well."
Morrow (7-4) will be re-evaluated on Tuesday.
"(The injury is) probably substantial in terms of what he's dealing with right now," Farrell said. "Just how he continued to tighten up after he came out of the game. He was in considerable pain. There will be further imaging, further testing in the morning."
Edwin Jackson (3-3) threw eight solid innings for the Nationals, giving up four hits and two earned runs.
Adam LaRoche hit a two-run homer, Rick Ankiel added a solo shot and Harper had three singles and a walk for the Nationals, who won their fourth in a row against a Toronto bullpen that was forced to use five pitchers in Morrow's absence.
Colby Rasmus and Yan Gomes homered for the Blue Jays.
Jackson departed after Edwin Encarnacion led off the ninth with a double.
"Just an unbelievable performance," Harper said of the Nats starter. "He had everything working for him, his fastball was good, his curveball, his changeup. He was really effective tonight."
Sean Burnett replaced Jackson and gave up a two-out, pinch-hit home run to Gomes before getting J.P. Arencibia to ground out to end the game.
Chad Beck came on for Morrow in the first and gave up a single to Harper to score Steve Lombardozzi, who was at second after a leadoff double.
"That's never happened to me before," Harper said of the delay during his at-bat. "That was kind of weird. It was kind of weird to go back up there and get into the zone again and get comfortable."
Harper went to third when first baseman David Cooper was charged with an error on Ryan Zimmerman's hard-hit ball. Michael Morse followed up with a sacrifice fly to score Harper.
Beck, who has been closing with triple-A Las Vegas and has usually been limited to one inning with the Jays, lasted 3 2-3 innings before being replaced by Luis Perez with two out in the fourth. Beck allowed three runs, two earned and after the game was returned to Las Vegas.
The Blue Jays called up left-handed pitchers Evan Crawford and Aaron Laffey and will make another move on Tuesday.
"I know what it does to your bullpen so I was sympathizing with (Farrell)," Nationals manager Davey Johnson said. "Not a whole lot, but I was sympathizing with him."
The Blue Jays (31-30) got one back in the bottom of the first on the ninth homer of the season by Rasmus.
LaRoche hit his 11th home run of the campaign to make it 4-1 with two outs in the third after Harper walked.
The Nationals (36-23) scored once in the seventh after loading the bases on three singles, starting with a bunt down the third-base line by Lombardozzi.
Ian Desmond scored Lombardozzi with a two-out single against Jason Frasor, but the Nationals left the bases loaded.
Ankiel, who entered the game in the seventh to play centre field, hit his fourth homer of the season to lead off the eighth against Francisco Cordero.
Notes: Attendance at Rogers Centre was 18,513. ... Washington centre-fielder Roger Bernadina came out of the game in fourth inning with a strained right hamstring after going first to third on a wild pitch. He was replaced by Xavier Nady. Harper moved from right field to centre and Nady played right field. Harper moved back to right when Ankiel entered the game and replaced Nady. ... Harper was thrown out at third by right-fielder Jose Bautista in the fifth while trying to go first to third on a single. ... Vladimir Guerrero, who is on a minor-league contract at triple-A Las Vegas, was back in the starting lineup Monday after missing one game after he was hit by a pitch on the left hand on Saturday. He was batting .214 (6-for-28) with two RBIs in seven games since being called up from single-A Dunedin on June 2 ... Washington's Chien-Ming Wang (1-2, 5.11 earned-run average) will face Toronto's Henderson Alvarez (3-5, 3.76 ERA) on Tuesday.Suggest a correction