Cubs-Cardinals is perhaps the best rivalry in the game, better even than Red Sox-Yankees or Dodgers-Giants. The St. Louis Cardinals and Chicago Cubs have never been this good in the same season, winning 100 and 97 games, respectively.

Now they'll play against each other in the postseason for the first time. Get used to it. They'll probably face each other in October many times going forward.

Here are five questions.

1. What is the health of Cardinals catcher Yadier Molina?

He will play despite having a torn ligament in his left thumb. He will protect that thumb with a special brace, one designed to cushion it against the ball slamming into his catcher's mitt 150 times or so every game. Molina is as tough and as durable as they come, and he is the most important player on the Cardinals. His impact behind the plate -- running the game and pitching staff -- cannot be overstated. No catcher in the game is quite like him. If he can play well, the Cardinals can beat anyone. If he can't, they can't.

2. What kind of roll are the Cubs on?

They have won nine games in a row, including their victory over the Pirates in the NL wild-card game, and have outscored their opponents 38-9 during that stretch.

Their starting pitching, not just the incomparable Jake Arrieta, has been stunningly good. In its final eight regular-season games, the Cubs' rotation allowed two runs in 51 1/3 innings: In the past 101 years, no rotation other than the 2008 Indians has finished that strong. Mix in Arrieta's performance against the Pirates, and it's two runs in 60 1/3 innings. Granted, most of that dominance came against teams that were done and terrible this season, but it's still impressive. And even though the Cubs won't have Arrieta available to start until Game 3 at home on Monday, Jon Lester will start Game 1. His résumé in October is impressive. And a game such as this is why the Cubs signed him in the offseason.

3. In what kind of shape is the Cardinals' rotation?

It was close to historically good for most of the season, but it appears to be not as good now. In a perfect world, the Cardinals would have started Michael Wacha in Game 1 and Carlos Martinez in Game 2 because they have the best stuff on the team and some of the best stuff in the game. But Martinez was recently shut down for the reason with shoulder stiffness, and Wacha tired down the stretch. He had a 7.88 ERA in five starts in September, walked 18 batters and gave up seven home runs in 24 innings. So John Lackey will start Game 1, which isn't bad. He has made some great starts in the postseason, and his ERA in September was 1.78.

4. Can anyone beat Jake Arrieta?

Arrieta had the lowest ERA (0.75) after the All-Star break since the All-Star Game was established in 1933. He had the lowest ERA ever from Aug. 1 on since earned runs became an official statistic just over 100 years ago. He had the lowest ERA by any starting pitcher ever in his final 20 starts of the regular season. His scoreless-innings streak is at 31. And in the NL wild-card game against the Pirates, he became the first pitcher in postseason history to throw a shutout with no walks and at least 10 strikeouts (he had 11).

In his past 13 starts, he has induced more ground-ball double plays than he has allowed extra-base hits. The Cubs are 14-0 in his past 14 starts. In his past 19 starts, the Cubs are 18-1, the lone loss being Cole Hamels' no-hitter on July 25. But, chances are, the Cardinals will see him only once, in Game 3.

5. What kind of offense can the Cardinals generate?

They were 11th in the National League in runs scored. Granted, it was the regular season, and everything, including home-field advantage, was wrapped up, but the Cardinals didn't hit much down the stretch, and were shut out in their final three games. The big question is the return to health of several key Cardinals who are battling injuries or coming back from injuries, led by Molina and Matt Holliday.

Manager Mike Matheny is going to have to mix and match, especially in the outfield, to find the right combination. He has lots of choices. The Cardinals appear to be too banged up to be at their best right now, and they are running into a team, an archrival, with tremendous momentum. But remember 2006, when the Cardinals hobbled into the postseason without much of a chance of winning, and wound up winning the World Series. They have done other similar things in recent years.

Cardinals in five.