On Saturday the Red Sox faced the possibility of losing hold of sole possession of first place. A loss to the Yankees and a Tampa Bay victory would mean that the top of the AL East was once again even. But that outcome did not come to pass thanks in no small part to a member of the roster who has had a far larger than expected role in the Sox’ season spent almost entirely in first. John Lackey the Red Sox’ de facto ace for much of the season had given fans a bit of a scare this month by pitching through a rolled ankle against the Astros on Aug. 5 then getting hit around out of the games in his start six days later against the Royals. But Saturday afternoon at Fenway Park facing a Yankee lineup much improved over the version he saw just under a month ago a crowd of 37517 saw what was arguably Lackey’s best performance in at least a month in a 6-1 win over New York. The right-hander shut down New York batters for 6 2/3 strong innings allowing one run on six hits and three walks. John Farrell gave him a chance to finish the seventh but after Lackey walked Eduardo Nunez — who granted was quickly erased by a double play — and drilled Chris Stewart lefty Craig Breslow came on to finish the frame. Lackey ended his day having thrown about two-thirds of his 103 pitches for strikes and although he recorded only one strikeout — his lowest total since Sept. 4 2011 — he was effective in other ways namely getting ground balls. Fifteen of Lackey’s 20 outs came on grounders. The top third of the Yankees lineup consisting of Brett Gardner Ichiro Suzuki and Robinson Cano was particularly hapless against Lackey. The trio combined to go 0-for-11 with six men left on base. Lackey struggled the most in the fifth and seventh innings both of which followed lengthy Red Sox rallies that caused him to sit on the bench a little longer than normal. During the first test Dustin Pedroia made a pair of pretty plays to help Lackey escape the jam and during the seventh Lackey’s evening ended before he had a chance to get the last out. It was an important return to form after he allowed four earned runs — all in the first four innings — against Kansas City his last time out. Lackey’s ERA on the season is down to 3.22.