In their tough 5-4 loss in Vancouver, the Oilers not only lost the first game of the series. At some point in the second period, they lost one of their best players: Leon Draisaitl.
He had to leave the game in the second period, after he jumped on the ice for a few seconds before returning to the bench, and eventually, the locker room.
Of course, in the playoffs, we don't often see teams tell the truth regarding injuries. It's possible that Draisaitl was truly dealing with cramping issues, but it could be much more serious than that.