Jose Guillen was also in the outfield after being the designated hitter on Sunday because of a sore left shin. Guillen, who played right field, finished the series 9-for-16, hitting the decisive solo homer in the ninth inning of Monday's 3-2 victory.
"[The] swelling is down. [He] should be OK to roam the outfield," Royals manager Trey Hillman said.
Hillman felt that Gathright's catches, two near the center-field wall and the dive in right-center, probably saved several runs.
"It's good to have him running around out there in the outfield," he said.
David DeJesus, the center fielder most of this season, was in left.
"Once you compare him with Joey in center field, it comes down to pure speed," Hillman said. "It's not an issue of whether or not David is a good center fielder, it's an issue that Joey has the ability on any given day to be a great center fielder and make a huge impact, like he did three different times [Sunday]."
Guillen went into Monday's game 7-for-12 with three homers and nine RBIs in the first three games of the series and, naturally, Hillman was asked about the hot streak.
"Hot is the operative word," Hillman said. "When he's in warmer weather, which he prefers, he's a lot better. He doesn't like cold weather."
It's been boiling hot in New York and, in the Royals' other very warm series at Miami on May 16-18, Guillen went 6-for-12 with eight RBIs and a homer.
Hillman decided to put Guillen in right and DeJesus in left at Yankee Stadium for a reason in addition to Guillen's rocket arm.
"Primarily because Jose actually feels more comfortable over there, and left field is bigger and David is faster, so it makes sense," Hillman said.