Yea, we've seen Cooper quickly get the Lightning back in gear after an embarrassing first game a few times now, so I wouldn't count them out at the moment. The "rust" factor was also probably in play last night.
Expected goals were 4.42 to 3.08 in favor of Tampa in all situations. Obviously a lot of that advantage came in "garbage time" play when the Rangers sat back after their great 2nd period effort and the early goal to start the 3rd. But I'd expect the Bolts to clean up a lot of their defensive lapses going forward. (Although I think they've been weak in that area all year - the Bruins were able to dissect them pretty well in the regular season.) But they have the shooters who can beat Shesterkin if given the same rate of high-danger chances - 20 total for Tampa last night.
In fairness to the Rags, they've been bucking the expected goals model for the entire season with high shooting percentage and great goaltending. Montreal made it to the Cup final last year playing a similar game, and New York is certainly a much better squad than the Habs were.