Running back Darren Sproles, above, along with Pierre Thomas and Chris Ivory, each have roles in the Saints’ running game, which is successful enough to open up the field for the team’s record-setting passing attack. (Chris Graythen/Getty Images)

The statistics compiled by Drew Brees this season — NFL single-season records in passing yards (5,476) and completion percentage (71.2) chief among them — are impressive enough to distinguish the New Orleans Saints signal-caller even in the age of the quarterback.

But Brees spent nearly one-fourth of his postgame news conference after Saturday’s win commending an undrafted, injury-prone running back. He also reportedly helped recruit a 5-foot-6 quicksilver back — currently the NFL’s shortest player — as a free agent last offseason. And he makes no secret of his appreciation for an undrafted power back whose college career ended at a Division II school.

The worst-kept secret in the Saints’ locker room is that the team’s running game, ranked sixth in the NFL, is not merely capable of providing balance for Brees’s aerial pyrotechnics. The unassuming threesome of versatile Pierre Thomas, explosive Darren Sproles and powerful Chris Ivory provides the Saints with another dangerous offensive threat.

“That,” tight end Jimmy Graham said, “is what makes this offense so special. We are well-rounded.”

The last time the Saints lost a playoff game — a 41-36 defeat last January at the Seattle Seahawks — Thomas and Ivory were sidelined with injuries and Sproles had yet to arrive. But the trio, who helped the Saints amass 167 rushing yards in the wild-card-round victory over the Detroit Lions, will play important roles in Saturday’s NFC divisional playoff on the road against the San Francisco 49ers.

Moving the ball on the ground will be a challenge against San Francisco, which allows just 77.2 rushing yards per game, 15 yards fewer than the league’s second-best rushing defense, Baltimore.

But even with the loss of Mark Ingram, the 2011 first-round pick who recently was placed on injured reserve, the Saints have a deep stable of backs who play complementary roles. None of the three collected more than 603 yards and five touchdowns on the ground this season.

“We all have different types of skills,” said Thomas, who was second to Ingram with 110 carries during the regular season. “. . . We have to show the coaches that this ground game of ours is powerful.”

Thomas, signed as an undrafted rookie free agent out of Illinois in 2007, played a key role in the Saints’ Super Bowl-winning season two years ago. After leading the team in rushing yards in 2009, Thomas scored two touchdowns and converted a crucial fourth-and-one play in overtime of the Saints’ NFC title game victory. In the Super Bowl, Thomas had a 16-yard touchdown on a screen pass against the Indianapolis Colts.

Thomas was on injured reserve when the Saints lost to the Seahawks in the playoffs. But in his first playoff game since the Super Bowl, Thomas rushed for 66 yards on just eight carries Saturday and added 55 receiving yards. He spent most of the night spinning by defenders and breaking tackles.

“I couldn’t believe he stayed up,” left guard Carl Nicks said of one run. “. . . We are a different team when that guy is healthy.”

Brees said he has never played with someone “who is tougher, smarter or more versatile” than Thomas, adding that he “could not help but notice the way he ran, shedding tacklers one after another, getting the tough yards. It was phenomenal.”

Thomas, who has long distinguished himself with yards gained after the catch, said one of his rules is not to let the first tackler take him down.

“I try to break as many tackles as I can and get in that end zone,” he said. “Everyone tells me that I have freaky balance, but it’s the gift that God gave me.”

The Saints’ big-play back is Sproles, who set a single-season NFL record for all-purpose yardage (2,696) in his first season in New Orleans. Sproles also led the team in rushing yards (603), was second in receptions (86) and ranked among the league’s leaders in yards after catches. He scored two touchdowns Saturday.

Brees knew what the Saints were getting when they signed the 190-pound Sproles. Brees and Sproles were teammates when Sproles was a rookie with the San Diego Chargers in 2005.

“He walks in the room and you are stunned at the size and the stature,” Brees said. “This is a game for big, strong, fast guys. And you just say, ‘This guy does not belong.’ But he does. He more than belongs.”

Ivory went undrafted in 2010 after he was kicked off Washington State’s team for an alleged off-field incident and finished his career at Tiffin University in Ohio. Despite an unlikely path to the pros, he wound up leading the Saints in rushing yards last season while former back Reggie Bush and Thomas nursed injuries. But the 6-foot, 222-pounder suffered a foot injury late in the season and missed the playoff loss.

This season, Ivory missed the first seven games with an injury, but finished the regular season with 374 rushing yards and added 47 more on 13 carries against the Lions.

“The teams that can run the ball and have balance on offense are the teams that advance year in and year out,” wide receiver Marques Colston said. “San Francisco has been playing well all year. But we are hitting our stride.”