Arizona Diamondbacks at Boston Red Sox: Final Score & Recap

The Boston Red Sox defeated the Arizona Diamondbacks 9-4 at Fenway Park on August 18, 2026, in a game that swung decisively in the third inning despite an early jolt from Arizona. The DiamondIQ model entered the night giving Boston a 56 percent chance of winning, and by the final out that figure had reached 100 percent.

The third inning was the fulcrum of the entire contest. Gabriel Moreno gave Arizona a lead with a home run off Ranger Suarez that represented the single largest win-probability swing of the game, shifting the outlook by 32.4 percent in the Diamondbacks' favor. However, Boston answered emphatically in the bottom half against Merrill Kelly. Adley Rutschman connected for a home run worth 11.2 percent in win probability, and an Andruw Monasterio pop out — recorded as a 7.7 percent positive swing for Boston in the context of the inning's sequencing — reflected how thoroughly the Red Sox had controlled the frame, scoring twice to claw back into the game and set the tone for what followed. Boston added single runs in the fifth and seventh innings along with two in the sixth, including a Mickey Gasper home run off Kevin Ginkel worth 8.0 percent in win probability, which pushed the lead beyond reach. Jordan Lawlar's strikeout against Tyron Guerrero in the sixth represented a 8.1 percent swing against Arizona, punctuating the D-backs' inability to generate any sustained response.

Among the top performers by the DiamondIQ model's estimates, Moreno led all batters with a WPA of plus-26.8 percent and an RE24 of plus-3.1, though his early impact was ultimately absorbed by Boston's offense. Monasterio finished at plus-15.8 percent WPA and Gasper at plus-14.6 percent WPA with an RE24 of plus-2.9, underscoring their contributions to the Red Sox attack. On the mound, Tyron Guerrero was the standout, posting a plus-11.4 percent WPA to pace Boston's pitching staff in a comfortable series victory at Fenway.