Left-hander Roenis Elias struggled in his fourth Major League start, while Alvarez baffled the Mariners' bats in a two-hitter in Seattle's 7-0 loss in front of 24,003 at Marlins Park.
"When you run into a guy who's got three or four pitches working, and he's a power pitcher, it's going to be tough," McClendon said. "I don't care who you are. If he's commanding three or four pitches and he's got plus-stuff on the fastball, you're probably going to have a long night. That's what it was. He pitched extremely well tonight."
Seattle couldn't muster much off Alvarez (1-2), who retired the first 15 batters through five innings. Seventeen of his outs were via grounders. He also struck out four batters and walked none.
Dustin Ackley ended the perfect-game bid on the first pitch of the sixth with a single to center. A double play off the bat of Mike Zunino allowed Alvarez to face the minimum until the catcher doubled down the third-base line with one out in the ninth.
Zunino was the only Mariners baserunner to reach scoring position, but he was stranded there after consecutive groundouts to second by Nick Franklin and Abraham Almonte to end the game.
"It's one of those things where [McClendon] wants us to be aggressive at the plate and hunting balls in the strike zone early and try to put good swings on them," said Zunino, who finished 1-for-3. "[Saturday] when you run into a guy that's got good cut to his fastball and good offspeed pitches, he was able to keep his pitch count down when we were able to get some [quick] outs."
Elias (1-2), meanwhile, surrendered a season-high six runs (four earned) on eight hits over 5 2/3 innings, with career highs in walks (five) and strikeouts (five).
After working out of trouble in the first two frames, Elias allowed an unearned run in each of the next two.
Christian Yelich led off the third with a double and raced to third when Almonte bobbled the ball once it bounced off the left-center-field wall. Elias struck out Marcell Ozuna and intentionally walked Giancarlo Stanton before Casey McGehee's one-out RBI single.
Adeiny Hechavarria and Donovan Solano produced back-to-back one-out singles in the fourth, and Alvarez bunted them over. Ball four to Yelich got past Zunino, permitting Hechavarria to race home.
Ozuna broke the game open with a three-run homer into the Clevelander pool in left field with two outs in the sixth. It would be the last pitch -- career-high No. 111 of the night -- for Elias.
"I felt a little tired, but I felt I could get out of that inning no problem," Elias said. "It was a high fastball. I was trying to go in on him and left it over the middle."
Hechavarria had singled with one out and advanced to third on Solano's groundout to third. Alvarez drove Hechavarria in with an RBI single to center. Yelich followed with a walk before Ozuna connected on a 2-2 fastball.
In their previous two games, Mariners starting pitchers combined for nine runs allowed on 13 hits in just five innings pitched.
"I thought he threw pretty darn good," McClendon said of Elias. "His command was a little shaky early, but he got it back together. It was unfortunate we were trying to push him a little bit because where we are with our bullpen. If you really think about it, he was one out -- the pitcher -- from having a fantastic outing, so it's a shame it ended up like it did. He did a great job.
During the Mariners' five-game skid, the offense has averaged just 2.4 runs per game, but the clubhouse isn't panicking despite three straight series losses.
After all, there are still 144 games remaining in the regular season. Look no further than the opposing dugout, where the Marlins had previously dropped eight in a row and nine of 10.
"Everybody does hit those rough patches, but I think that's what it is -- just a rough patch," said Brad Miller, who went hitless in three at-bats. "It doesn't really reflect the type of team we've got. Get back [Sunday], hopefully come here, take care of business, and get back home and keep things going."