But the Pirates slugger has a way of dramatically making negative stats moot. Alvarez did so Sunday, lashing a single to drive in the go-ahead run in a 5-3 victory at a raucous PNC Park that put the Bucs one win from advancing to the NL Championship Series.
Two were on base with a 1-1 count when Alvarez, whose swing is designed to lift balls high and far, rolled Siegrist's 95-mph fastball for a single between first and second base. Russell Martin followed with a run-scoring hit.
"He threw me a couple of fastballs out over the plate," Alvarez said. "I was able to make good contact on the ball and drive it into right field. But I just knew that it was going to be a battle. It was going to be a grind. In the past, the few times I've faced him, they've been very tough at-bats."
Siegrist thought he was tough enough on Alvarez.
"I was just really hoping to get a ground ball there," Siegrist said. "I thought I made a good pitch, and it found a hole. I looked at it ... just a good piece of hitting."
You'd think four seasons in the Majors, after being picked second overall out of Vanderbilt in the 2008 First-Year Player Draft and going through a highly publicized contract negotiation, is time enough to get to know someone. But often a volume of work leads to an avalanche of numbers and a difficulty in seeing what's important.
If the full body of stats could define a person, Alvarez would be pegged as an all-or-nothing swinger. He had 30 home runs in 2012, an NL-leading 36 in '13, but 180 strikeouts last season and a league-leading 186 this year. Alvarez's troubles against left-handed pitchers are documented by his .200 career regular-season average against them.
But put a guy in a playoff race and on the bright stage, and if he's who you think he is, the cheering of the crowd will clear the warts in a hurry. Alvarez is looking clean and clear these days.
The game-winning hit raised Alvarez's postseason batting average to .400 (4-for-10) with plenty of power -- two home runs, a double and four RBIs. Now even his work against lefties can be analyzed through a new prism.
Siegrist, a rookie, posted a 0.45 ERA this year, with 43 of his 45 appearances ending scoreless. He held lefty hitters to a .118 batting average (8-for-68). Siegrist is the type of guy paid to frustrate someone like Alvarez. However, Alvarez drove in 13 runs against lefty relievers in just 39 at-bats this season, compared to 11 RBIs in 94 at-bats against lefty starters. The later in the game, the bigger the moment, the better Alvarez's at-bats become.
"Honestly, he was kind of rushed to the big leagues, because of where he was drafted and because of the contract that he signed," Pirates center fielder Andrew McCutchen said. "So he had to learn in the Major Leagues. So I mean, if you ask anybody who has played here and anybody who has played the game -- it's tough to learn here. But he's done that and he's done a great job, and he's going to continue to keep getting better."
On Sunday, Alvarez struck out in his first two at-bats, yet the Cards feared him enough to walk him and load the bases with the score tied at 2 in the sixth. Martin followed with a sacrifice fly.
With the score tied again, Cardinals manager Mike Matheny didn't hesitate to count on Siegrist to continue his success. But Bucs manager Clint Hurdle has seen enough of Alvarez's thirst for big at-bats to know he'd relish the confrontation.
"[It was a] very impressive at-bat tonight late, left on left, after a challenging start to the game," Hurdle said. "He is a very competitive young man, and he really doesn't let one at-bat fall into the next. You might get the same result, but he's able to move from at-bat to at-bat, from inning to inning on defense.
"He's trying to make adjustments. And I think we're seeing a lot of those adjustments more so this year than maybe we have in the past, and we're seeing some in the postseason. They get your attention."
Nobody's talking about Alvarez's .235 career regular-season batting average these days. The .233 and the high strikeouts this season weren't all that important either, definitely not to Hurdle, and certainly not to the fans waving black towels and flags at PNC Park. And certainly not to the Cards, who elected to walk Alvarez in the sixth rather than go with a history that says they'll get him out with a tough lefty.
In the eighth, when it mattered most, the Cardinals challenged Alvarez and ended up one loss from the end of their season.
"It's been a lot of fun," Alvarez said. "The atmosphere, the energy has been outstanding. And that's what you dream of -- to be able to play these type of kind of caliber games at this time of year. And to do it here, you know, it's just been a lot of fun."