Heading into Tuesday night's NHL action -- a busy night, with 12 games on the schedule -- there are three teams that still boast a perfect record: the San Jose Sharks, the Colorado Avalanche, and the St. Louis Blues. But by the end of the night, there will be at least one fewer, as one of those dozen games features the unbeaten Sharks and Blues facing off in St. Louis.

It's a battle of the unbeatens, and in the words of Highlander, there can only be one.

Here are five things to know about this marquee matchup:

1. Both teams are scoring in bunches.

Yes, both of them. The Blues and Sharks are the only two teams in the league averaging over four goals a game. The Sharks are the league's highest-scoring team, with a goals per game average of 4.8 through their first five contests, but the Blues, typically a low-scoring club, are suddenly potting goals left and right. They're right behind San Jose at 4.75.

2. But lest you think this will be a high-scoring game...

Both teams are also among the best clubs in the NHL defensively early in the season. The Sharks are allowed just 1.4 goals per game, second only to the Colorado Avalanche. The Blues sit in fourth in the category at 1.75. In other words, neither team is winning their games close. San Jose and St. Louis are outscoring opponents like crazy, with 5-on-5 goals for/against ratios of 4 and 3.67, respectively.

3. Battle of the top lines.

The Sharks have a combined 19 points from their top line of Joe Thornton, Brent Burns, and Tomas Hertl. The Blues, meanwhile, have 18 points from their top line of Alex Steen, David Backes, and T.J. Oshie. One suspects these lines will go head-to-head; the winner of this matchup could decide the game.

Fortunately for San Jose, they won't have to make any adjustments to theirs. Tomas Hertl, the NHL's third-leader scorer -- tied with three other players, including the aforementioned Steen -- suffered nasty hits in both of his last two games, first getting his head picked on a hit from Alex Edler of the Vancouver Canucks, and then in a collision with Clarke MacArthur of the Ottawa Senators. Hertl stayed in the game after the Edler hit; he left the Ottawa game, and spent the next few days under observation. But Hertl is expected to be in the lineup.

4. The Blues' powerplay is crushing it right now.

The Blues have six powerplay goals in just 16 opportunities, good for a league-best success rate of 37.5%. Something tells me that will come down, but it would behoove San Jose not to tempt fate, especially on the road.

5. Home-ice advantage is noteworthy.

And speaking of being on the road, you should probably know that, of the nine games these two teams have played thus far, just one has been on the road. The Blues have still yet to leave the Scottrade Center, and the Sharks have played just one game away from San Jose's SAP Center. Is it possible that a slightly more mixed schedule to open the year would have led to slightly more mixed results? A St. Louis win tonight in their fifth-straight home game would give that theory a little more credence.