Chicago Cubs vs Seattle Mariners Prediction, Preview and Odds - 08/21/2026

Game Time: 10:10 pm ET, Friday, August 21, 2026

Venue:  T-Mobile Park, Seattle, WA

Where to Watch:  MLB TV

DraftKings:  Moneyline odds:  Cubs -112, Mariners -108; Over/Under:  8 runs

Bet365:  Moneyline odds:  Cubs -110, Mariners -110; Over/Under:  8 runs

BetMGM:  Moneyline odds:  Cubs -110, Mariners -110; Over/Under:  8 runs

Chicago Cubs:  74-54 (2nd place, NL Central)

Seattle Mariners:  60-67 (3rd place, AL West)

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Chicago Cubs:  6-4 last 10

Seattle Mariners:  4-6 last 10

The Cubs are entering this series off a loss and won their 3-game series against the Chicago White Sox 2-1 in their last series. They enter this game with a 74-54 record overall and have a road record of 36-27. This is the series opener of a 3-game series with the Mariners on Friday and they have Thursday off as a day of rest. Their offense ranks 3rd in the MLB with a .755 OPS. Clay Holmes was their starting pitcher on Wednesday while Matthew Boyd is making his start in this game on Friday. He is 8-2 with a 4.02 ERA this season. His team won 2 of their last 3 games this season with him making an appearance. In his last MLB regular season appearance, he allowed 7 ER, 4 HR, and 3 BB with 2 SO on 5 hits through 5.1 IP against the St Louis Cardinals.

The Mariners are entering this series off a loss and lost their 3-game series against the Milwaukee Brewers 2-1 in their last series. They enter this game with a 60-67 record overall and have a home record of 33-29. This is the 1st game of a 3-game series with the Cubs on Friday. Their offense ranks 27th in the MLB with a .686 OPS. George Kirby was their starting pitcher on Thursday while Emerson Hancock is making his start in this game on Friday. He is 7-7 with a 3.30 ERA this season. His team lost 4 of their last 5 games this season with him making an appearance. In his last MLB regular season start, he allowed 2 earned runs, 1 homer, and 2 walks with 8 strikeouts on 5 hits through 7 innings pitched against the Houston Astros.

The current betting odds have the Cubs listed as a slight favorite in this game according to Draftkings Sportsbook. The Cubs have looked really good in their games this season with their 74-54 record overall which has them right near the top of the NL Central. They have been a good road team too with their 36-27 road record this year. Meanwhile, the Mariners haven't looked good in their games this season with their 60-67 record overall which has them right in the middle of the AL West. They have looked a lot better in their own ballpark though with their 33-29 home record this season. The Mariners are 4-6 in their last 10 games and they haven't looked good since the trade deadline with one of the worst offenses in MLB. The Cubs have one of the best offenses in the league this season and they have been rolling lately, now 6-4 in their last 10 games. The Cubs are going with Boyd in this one and he hasn't looked great this season. He is 8-2 with a 4.02 ERA, but the team has been having a ton of success with him. He did give up 7 earned runs in his last start, but that hasn't been a common theme for him and he will be looking to bounce back with a better start against this Mariners offense that hasn't looked good lately. The Cubs have also won 2 of their last 3 games with Boyd pitching. The Mariners are going with Hancock in this one and he hasn't looked bad this season. He is 7-7 with a 3.30 ERA, but the team has had a lot of trouble with him lately. He only gave up 2 earned runs in his last start, but the team has lost 4 of their last 5 games with him starting. The Cubs are not only the hotter team here, but they also have the much stronger offense this season and the Mariners have been giving up a lot more runs lately too. The best way to place a bet here is on the Cubs to win this game. 

Cubs Mariners Prediction:  Our MLB Pick for Friday, August 21, 2026 (10:10 pm ET start time) is Cubs 6 Mariners 3.

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Chicago Cubs: 254-206 (+20.1 units) on the moneyline in all games. 117-111 (+8 units) on the moneyline in road games. 78-59 (+10.1 units) on the moneyline in an inter-league game. 7-4 UNDER against AL West opponents.

Seattle Mariners: 241-223 (-21.8 units) on the moneyline in all games. 129-124 (-25.6 units) on the moneyline when the money line is -100 to -150. 68-64 (-5.7 units) on the moneyline in an inter-league game. 15-6 UNDER at home when the money line is +125 to -125.

Chicago Cubs:  K. Gausman (SP) Day To Day - Hand. P. Maton (RP) Sixty Day IL - Knee. E. Cabrera (SP) Fifteen Day IL - Blister. D. Swanson (SS) Ten Day IL - Side. D. Palencia (RP) Sixty Day IL - Elbow. B. Brown (RP) Sixty Day IL - Neck. G. Hollowell (RP) Fifteen Day IL - Shoulder. M. Shaw (RF) Ten Day IL - Hand. H. Milner (RP) Fifteen Day IL - Appendicitis. R. Martin (RP) Sixty Day IL - Elbow. P. Hodge (RP) Sixty Day IL - Elbow. C. Horton (SP) Sixty Day IL - Forearm. H. Harvey (RP) Sixty Day IL - Tricep. J. Steele (SP) Sixty Day IL - Elbow. T. Austin (1B) Sixty Day IL - Knee. S. Miller (RP) Sixty Day IL - Elbow.

Seattle Mariners:  C. Emerson (SS) Ten Day IL - Wrist. C. Sulser (RP) Fifteen Day IL - Oblique. L. Raley (RF) Sixty Day IL - Elbow. J. Crawford (SS) Ten Day IL - Wrist. W. Wilson (3B) Sixty Day IL - Thumb. M. Brash (RP) Fifteen Day IL - Lat. C. Criswell (RP) Sixty Day IL - Shoulder. C. Vargas (RP) Sixty Day IL - Lat. L. Evans (SP) Sixty Day IL - Arm.

“I thought he was really good. Breggy had a great game at third base, I thought, on defense. But, the ball was on the ground. I thought he pitched very, very well.” - Craig Counsell after his team’s loss against the White Sox in their game on Wednesday. 

“That kind of a start there, to get the guys on base, I thought Taylor Ward picking up a two-RBI single was huge. Just up and down, you’re so much more balanced. I think [Donovan] sets the tone at the top and allows guys below him to drive him around.” - Dan Wilson after his team’s win against the Brewers in their game on Wednesday.

Pete Crow-Armstrong (L) DH

Seiya Suzuki (R) RF

Alex Bregman (R) 3B

Michael Busch (L) 1B

Nico Hoerner (R) SS

Pedro Ramírez (S) 2B

Carson Kelly (R) C

Ian Happ (S) LF

Tyrone Taylor (R) CF

Brendan Donovan (L) 3B

Randy Arozarena (R) LF

Dominic Canzone (L) RF

Julio Rodríguez (R) CF

Josh Naylor (L) 1B

Taylor Ward (R) DH

Cole Young (L) 2B

Jhonny Pereda (R) C

Brock Rodden (S) SS

Batting Average:  Justin Dean (.375)

Hits:  Pete Crow-Armstrong (136)

Home Runs:  Pete Crow-Armstrong (31)

RBI:  Pete Crow-Armstrong (79)

Stolen Bases:  Pete Crow-Armstrong (31)

Wins:  Colin Rea (8)

Saves:  Jacob Webb (9)

ERA:  Ty Blach (0.00)

Batting Average:  Brock Rodden (.294)

Hits:  Josh Naylor (124)

Home Runs:  Dominic Canzone (19)

RBI:  Cole Young (56)

Stolen Bases:  Josh Naylor (25)

Wins:  Logan Gilbert (10)

Saves:  Andrés Muñoz (23)

ERA:  Matt Brash (0.54)

Managers:

Chicago Cubs: Craig Counsell (3rd season)

Seattle Mariners: Dan Wilson (3rd season)