Mariners vs Royals Prediction, Odds, Moneyline, Spread & Over/Under for May 23

Odds updated as of 4:12 a.m.

MLB action on Saturday includes the Seattle Mariners facing the Kansas City Royals.

All the information you need to make smart wagers on this game at FanDuel Sportsbook can be found below. Check out all of the latest MLB betting lines here.

Seattle Mariners (25-27) vs. Kansas City Royals (20-31)
Date: Saturday, May 23, 2026
Time: 4:10 p.m. ET
Venue: Kauffman Stadium — Kansas City, Missouri
Coverage: Fox Sports 1, Royals.TV, and Mariners.TV

All MLB odds, betting lines and prop bets are available on FanDuel Sportsbook.
Moneyline: SEA: (-142) | KC: (+120)
Spread: SEA: -1.5 (+116) | KC: +1.5 (-140)
Total: 8.5 — Over: (-122) | Under: (+100)

Mariners vs Royals Probable Starting Pitchers

Probable Pitchers: George Kirby (Mariners) – 5-3, 3.45 ERA vs Stephen Kolek (Royals) – 2-0, 4.24 ERA

The probable pitchers are George Kirby (5-3) for the Mariners and Stephen Kolek (2-0) for the Royals. Kirby’s team is 5-5-0 against the spread this season in his starts. Kirby’s team has won 60% of his starts when they are favored on the moneyline (6-4). The Royals have gone 2-1-0 against the spread when Kolek starts. The Royals were the underdog on the moneyline for two Kolek starts this season — they won both.

All MLB win probability predictions and picks are according to numberFire.
Prediction: Mariners win (59.4%)

Kansas City is a +120 underdog on the moneyline, while Seattle is a -142 favorite on the road.

The Royals are +1.5 on the spread (-140 to cover), and Seattle is +116 to cover the runline.

The over/under for Mariners-Royals on May 23 is 8.5. The over is -122, and the under is +100.

Bet on Seattle Mariners vs. Kansas City Royals on FanDuel today!

The Mariners have been favorites in 48 games this season and have come away with the win 24 times (50%) in those contests.
This season Seattle has come away with a win 14 times in 25 chances when named as a favorite of at least -142 on the moneyline.
The Mariners and their opponents have gone over in 23 of their 52 games with a total set by sportsbooks this season.
The Mariners have posted a record of 19-33-0 against the spread this season.
The Royals are 8-15 in games they were the underdog on the moneyline (winning 34.8% of those games).
Kansas City has gone 2-3 when playing as a moneyline underdog with odds of +120 or longer (40%).
In the 48 games oddsmakers have set an over/under for the Royals, they have combined with opponents to go over the total 21 times (21-27-0).
The Royals have gone 20-28-0 ATS this season.

Randy Arozarena leads Seattle with 55 hits and an OBP of .394, plus a team-best slugging percentage of .462. He’s batting .299.
Among all qualifying batters in MLB, he ranks 14th in batting average, eighth in on-base percentage, and 47th in slugging.
Julio Rodriguez is hitting .261 with 11 doubles, eight home runs and 17 walks. He’s slugging .430 with an on-base percentage of .323.
Among qualifying batters, his batting average places him 68th, his on-base percentage 89th, and his slugging percentage 66th.
Rodriguez has picked up at least one hit in four straight games. During his last five outings he is batting .316 with two doubles, a home run, a walk and an RBI.
Josh Naylor has collected 47 base hits, an OBP of .317 and a slugging percentage of .356 this season.
J.P. Crawford has six home runs, 16 RBI and a batting average of .204 this season.

Royals Player Leaders

Bobby Witt Jr. has racked up an on-base percentage of .363, a slugging percentage of .473, and has 59 hits, all club-highs for the Royals (while batting .294).
Including all qualified hitters in the big leagues, his batting average places him 21st, his on-base percentage is 36th, and he is 40th in slugging.
Maikel Garcia is hitting .260 with 13 doubles, a triple, three home runs and 19 walks. He’s slugging .383 with an on-base percentage of .323.
He ranks 71st in batting average, 89th in on-base percentage and 103rd in slugging percentage in MLB.
Vinnie Pasquantino has four doubles, two triples, five home runs and 22 walks while batting .197.
Salvador Perez is batting .206 with five doubles, eight home runs and nine walks.

5/22/2026: 2-0 SEA (Favorite: Mariners, Spread: -1.5, Total: 8.5, Favorite Moneyline: -118, Underdog Moneyline: +100)
5/3/2026: 4-1 KC (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -116, Underdog Moneyline: -102)
5/2/2026: 3-2 KC (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -142, Underdog Moneyline: +120)
5/1/2026: 7-6 KC (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -148, Underdog Moneyline: +126)
9/18/2025: 2-0 SEA (Favorite: Mariners, Spread: -1.5, Total: 9, Favorite Moneyline: -120, Underdog Moneyline: +102)
9/17/2025: 7-5 KC (Favorite: Royals, Spread: -1.5, Total: 8.5, Favorite Moneyline: -124, Underdog Moneyline: +106)
9/16/2025: 12-5 SEA (Favorite: Mariners, Spread: -1.5, Total: 8.5, Favorite Moneyline: -136, Underdog Moneyline: +116)
7/3/2025: 3-2 KC (Favorite: Mariners, Spread: -1.5, Total: 7.5, Favorite Moneyline: -120, Underdog Moneyline: +102)
7/2/2025: 3-2 SEA (Favorite: Mariners, Spread: -1.5, Total: 7, Favorite Moneyline: -166, Underdog Moneyline: +140)
7/1/2025: 6-3 KC (Favorite: Mariners, Spread: -1.5, Total: 8, Favorite Moneyline: -138, Underdog Moneyline: +118)