The St. Louis Cardinals are the consensus best team in baseball right now. They have the best record, the best run differential and they've topped ESPN's Power Rankings in four of the past five weeks.

But they better keep an eye on those pesky Pittsburgh Pirates, who are hanging in there, 6.5 games behind the Cardinals after beating the Brewers 2-0 on Wednesday behind Charlie Morton's 7 1/3 scoreless innings.

There's one obvious reason to believe the Pirates can catch the Cardinals: The two teams rank 1-2 in the majors in run prevention. There's another reason, however, to believe in the Pirates that requires digging a little more into the numbers.

FanGraphs tracks BaseRuns, which is simply bases accrued on offense and bases given up on defense. Given normal sequencing of events you can then project an expected record. It's a little better method for evaluating true talent than just looking at a team's runs scored and runs allowed.

Led by Gerrit Cole and his 1.73 ERA, the Pirates appear to have one of baseball's deepest rotations. Eric Hartline/USA TODAY Sports

Anyway, heading into Wednesday's games (the Cardinals beat the Rockies 4-2), the Cardinals' projected BaseRuns record was 33-26 compared to their actual record of 38-21. The Pirates' projected BaseRuns record was 33-25 compared to their actual record of 31-27. This suggests the Pirates, at the level of hits and home runs and walks and strikeouts and all that, have played just as well as the Cardinals. The Cardinals, however, have had better sequencing of events. If you wish, you can call that clutch. If you believe in clutch -- and with the Cardinals, given all their success through the years, it is admittedly difficult to suggest they've simply had better "luck" than the Pirates -- then you'll believe the Cardinals will continue to outplay their BaseRuns.

But I prefer to view it as the two clubs having a similar talent level. Of course, the Cardinals have already banked that 6.5-game lead, and that's huge. The Cardinals, however, despite that best record in baseball, have some serious questions right now:

Staff ace Adam Wainwright is out for the season. So far, they haven't really missed him, as Michael Wacha has been terrific, Carlos Martinez has stepped up and Lance Lynn and John Lackey have been very good. The bullpen hasn't blown a lead after the seventh inning. But can we expect the staff to continue allowing 2.95 runs per game? Unlikely. Even the 2011 Phillies -- with Roy Halladay, Cliff Lee and Cole Hamels -- allowed 3.27 runs per game. The 1968 Cardinals, in the Year of the Pitcher, with Bob Gibson posting a 1.12 ERA, allowed 2.91 runs per game. In other words, the Cardinals' run prevention has been insane so far. At some point, you have to think Wainwright's injury will affect them.

Matt Holliday and Matt Adams on the DL. Adams wasn't playing that well, but it does take a potential power bat from a lineup that is 13th in the NL in home runs. Holliday just landed on the DL with a partially torn quad, and while the Cardinals have good outfield depth with Peter Bourjos and Randal Grichuk, those two aren't going to post a .417 OBP like Holliday was putting up. If Holliday's injury lingers for more than a few weeks, I think they'll miss his presence in the middle of the order.

Yadier Molina's bat is in decline. He's hitting .279, but he hasn't homered and has scored just 12 runs.

Anyway, this is supposed to be about the Pirates, not the Cardinals. Here's something I like about them moving forward. Going through the lineup, nobody has really played above expectations yet, with the possible exception of catcher Francisco Cervelli, who is hitting .325/.402/.396. We can expect the lineup to improve and that's important to note because the Pirates are already keeping pace on offense with the Cardinals, averaging 4.11 runs per game to St. Louis' 4.0.

Gerrit Cole (1.73 ERA) and A.J. Burnett (2.11 ERA) have anchored the rotation. Are they this good? I love Cole and he's certainly in the process of making The Leap, but I can't imagine he keeps that ERA below 2.00 all season. But he has the ability to remain a Cy Young contender. Burnett's career-low ERA is 3.30, although he's also walking fewer batters than he ever has. Both have relied on absurdly low home run rates and they rank sixth and 11th in the majors in strand rate, so there are numbers to suggest some regression is in order.

But not necessarily all that much. The rotation has also received a boost from groundball specialist Morton, who is now 4-0 with a 2.05 ERA in his four starts since coming off the DL. In those four starts he's recorded 59 groundball outs compared to eight flyball outs. In Wednesday's win, 65 of his 102 pitches were sinkers. It's a good one and with the Pirates' willingness to shift, they can set up their defense to support all those snake burners. Francisco Liriano is 3-5 but has a 3.25 ERA, making Morton one of the better No. 4 starters in the league right now. It's a better rotation than the Pirates had in 2013 and 2014.

Oh ... and Andrew McCutchen.