PITTSBURGH — As Mike Sullivan returned to Pittsburgh for the first time since he and the Penguins parted ways last April, the new Rangers coach had a more immediate problem than controlling whatever emotions he was dealing with in returning to PPG Paints Arena.

He was coming back to Pittsburgh to face a team that had shut out the Rangers in their season opener Tuesday at the Garden, and the Blueshirts would be without first-line center Vincent Trocheck, who the Rangers announced Saturday will be out for an extended period with an upper-body injury.

Trocheck, a Pittsburgh native, left Thursday’s road win over Buffalo in the second period. The Rangers said Saturday that he will be out on a week-to-week basis.

“It sucks,’’ captain J.T. Miller said at Saturday’s morning skate. “He’s such a

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