The Senators have a 1053 PDO through 4 games, which has more than compensated for being outshot by an average of 6 shots per game, with the Canadiens carrying 54.5% of all shots fired in the series, in spite of Ottawa receiving more powerplay time.
The even strength possession game is more of the same, with the Canadiens holding a 53.1% edge in Fenwick.
Bringing scoring chances into the equation, the Canadiens have been even more dominant. Including all situations, the Habs have outchanced the Senators by about 4.5 per game, and have 56.3% of all scoring chances in the series. Using just even strength, the Habs have 3.5 more scoring chances per game, and have owned 56.5% of all scoring chances.
The Habs have fallen victim to the injury bug, bad officiating, and their own bad play at times, but the series is not yet over. Montreal has outplayed Ottawa by every important measure in underlying statistics, this series could turn around.
The only question now is, will it?