He proved that Wednesday night, holding his former team to three hits and one run over six innings in the Blue Jays' 5-1 victory.
Morrow was supported by home runs from Edwin Encarnacion to open the second, Adam Lind had a three-run shot in the third and Colby Rasmus led off the fourth with his second. The three home runs gave the Jays eight for the three-game series.
Morrow (9-7), who didn't allow a hit until there were two outs in the fourth, struck out a season-high 12. It's the fourth time this season he has fanned 10 or more.
"I've changed a lot in two years, not my pitching style necessarily," Morrow said, "but my ability to do what I want with the ball has improved. And my ability to stay in the zone and my ability to stay in the game."
This marked the first time Morrow had faced his former team in Seattle, which selected him in the first round of the 2006 draft. He was traded before the 2010 season for now Mariners closer Brandon League. He did not pitch in the Jays' visit last season.
"I don't think I necessarily pitched up to my ability when I was here," he said. "I've improved. I enjoyed my time here. It was sad to leave but it ended up to be a good move for both sides."
One pitch Morrow regrets throwing was a 97 mph fastball that hit Casper Wells in the face in the sixth inning. Wells, who had his streak of four home runs in four straight games ended, turned his head as the ball approached and was fortunate that it tagged the tip of his nose. Blood poured out as the trainer escorted him off the field. X-rays were negative.
"I couldn't tell live where it hit him and the way he reacted I was worried about him," Morrow said. "I'm glad he's all right."
Wells, with cotton balls stuffed up his nostrils after the game, said, "I have a headache. My nose feels humungous but I think I'll be all right."
Mariners manager Eric Wedge said Wells and the club "dodged a bullet."
"He should be OK. It hit him in the nose, so it was fortunate it wasn't broken," he said. "Anytime you get up there, it's scary."
Encarnacion hit a 1-2 pitch from Blake Beavan (3-4) for his 12th home run. Over his last 19 games, he's hitting .386.
Lind, also down in the count at 0-2, connected on his 22nd for a 4-0 lead after three. He has three home runs and 10 RBIs over his last eight games.
Beavan went just five innings, throwing 98 pitches. He allowed five runs on six hits. In his last two starts, he has allowed 11 runs and 17 hits in 11 1-3 innings.
"The way Brandon came through from the first pitch, he was extremely powerful," Jays manager John Farrell said. "He had his full assortment of pitches. Just an explosive fastball. To think where he's come from in two year's time. He has settled into a role here. He was overpowering for his six innings tonight."
Morrow acknowledged that there was "some extra incentive, some extra little adrenaline" pitching against his old team. He also was helped by the early lead, allowing him to be more aggressive.
"He had four pitches working," Wedge said. "He had a live fastball. It was jumping on us a bit. They made him work a little bit. That's probably why the ball got away from him late. He was wearing down a little bit."
Morrow held the Mariners hitless until two outs in the fourth when Mike Carp roped a clean single to right. Carp has been a tough out since he arrived from Triple-A July 19. The single extended his hitting streak to 17 games. He is hitting .379 with four home runs and 18 RBIs during the streak.
Carp also has reached base safely in 26 straight games.
The Mariners finally reached Morrow in the sixth. With one out, Ichiro Suzuki beat out an infield single. He moved to second on a wild pitch and came home on Franklin Gutierrez's double off the left-center wall.
The threat continued as Ackley walked. With two outs, Wells was hit by a pitch to load the bases. Adam Kennedy replaced him. Morrow then struck out Trayvon Robinson, looking, for his 12th.
NOTES: The Mariners finished off their July 30 trade with Detroit with the acquisition of RHP Chance Ruffin. He was the player to be named in the deal that sent RHP Doug Fister and RH David Pauley to the Tigers for Wells, LHP Charlie Furbush and INF Francisco Martinez. To make room on the roster, LHP Aaron Laffey was designated for assignment. Ruffin, 22, a supplement draft pick last June (48th overall), is the son of former big league pitcher Bruce Ruffin. ... C Miguel Olivo, hit on the chin by a foul ball Tuesday, did not start but was available to play for the Mariners ... Jays RHP Dustin McGowan, on a rehab assignment (shoulder surgery) with Double-A New Hampshire, threw four scoreless innings Tuesday, allowing just four hits with 57 pitches. "Next time out we'll look to increase by an inning or an additional 10 pitches," Farrell said. "The velocity is still there, up to 97. Another very encouraging and positive outing." ... The Jays play at Oakland Thursday and LHP Ricky Romero (11-9, 2.87 ERA) takes the mound. He has won four straight starts. ... the Mariners will travel to Tampa on their off day Thursday and will play the Rays in a three-game series beginning Friday. RHP Felix Hernandez (11-10, 3.38) leads it off.