First pitch went off under sunny skies and 86-degree heat at Fenway. Arizona grabbed an early edge with a 3-run 5th, but Boston answered right back with 3 of its own in the 6th to even it up, and that's where it stayed.
Both bullpens held after that — the score sat tied at 5 through the 9th, sending it to extras. Arizona broke through first in the 10th, plating 2, and Boston's answer stalled at 1. Final: Diamondbacks 7, Red Sox 6, with Arizona out-hitting the home team 10 to 9.
Boston still banks the series thanks to the first 2 games, but this finale is a different flavor of loss than the 2 lopsided ones that preceded it. Arizona, which had dropped 3 straight coming in, needed every bit of that extra frame to leave Fenway with a win instead of a sweep hanging over the flight home.
Neither club is walking away spotless — Boston's inching back toward health at a couple of spots (Isiah Kiner-Falefa, Trevor Story) while still missing key middle-of-the-order pieces, and Arizona's rotation remains a MASH unit with Zac Gallen and Corbin Burnes both still on throwing programs, not innings. Extra-inning wins like this one are nice mile markers, but they don't fix a depth chart.