Matheny's pregame prediction came true as the Cardinals pushed across nine runs over the first two innings on the way to an easy 12-2 triumph before 39,166 at Busch Stadium.
St. Louis won for the ninth time in its last 11 games. The Cardinals, who have won their last five home games, lowered their magic number for clinching the final playoff position to three. They lead the Los Angeles Dodgers by three games in the battle for the last Wild Card spot in the National League.
With five games remaining, the Cardinals largely control their own destiny.
"All we can do is worry about what we're doing," said right-hander Adam Wainwright, who picked up the win Friday with six strong innings. "If we go out and win all the games, then we're in good shape."
The St. Louis offense, which has struggled at times the past few weeks, caught fire at a perfect time. First baseman Allen Craig tied a career high with four hits in a brilliant 4-for-4 performance. Yadier Molina and Shane Robinson each slapped two-run homers.
The Cardinals (85-72), who managed just four runs over the last two games of a 4-2 road trip, erupted for nine runs over the first two innings against former teammate Edwin Jackson (9-11).
Nine of the first 14 St. Louis hitters scored during the early blitz.
Craig, who pushed his average to .313 from .306, said the day off Thursday proved to be the perfect tonic for the sluggish offense.
"It's a long season, and to get a day off right before the last homestand of the season is big," he said. "It's a great feeling to come home and come out of gates and put a good offensive performance together. We want to keep it rolling."
Wainwright (14-13) allowed just one first-inning run in improving to 10-6 at home. He surrendered five hits, struck out five and walked one.
"I wanted to buckle down," Wainwright said. "Tough pitcher, tough team, and we went out here and got a win. After those early runs, I just wanted to maintain my focus,"
Wainwright did just that while watching the offense put up its highest total since a 13-5 win against Houston on Aug. 23.
"That was one of the best offensive [games] we've seen in a long time," Matheny said. "We maximized the opportunities that we had."
The Cardinals were 5-for-12 with runners in scoring position and did most of the damage against Jackson, who had shut them out on four hits over eight innings in an 8-1 win 29 days earlier.
"It just wasn't a good day for Edwin," Washington manager Davey Johnson said. "He just couldn't locate."
Jackson gave up nine runs (eight earned) over 1 1/3 innings. He called his performance "disappointing and embarrassing."
The Cardinals tied a season high with five runs in the opening frame. They also scored five in the first inning of a 5-2 win over Miami on June 26.
Craig started the fireworks with a bases-loaded single to left in the first, scoring the first Cardinals run. Molina drove in a run when Washington third baseman Ryan Zimmerman was unable to handle his infield grounder. Carlos Beltran then drew a bases-loaded walk to push the lead to 3-1. Daniel Descalso added a run-scoring sacrifice fly and Pete Kozma drove in the final run of the inning with a single to right.
St. Louis put the game away with four more runs in the second. Jon Jay doubled and scored on a groundout by Matt Holliday. Craig followed with an RBI single before Molina homered for the second time in the last four games.
"This was big for all of us," Craig said. "We don't want to get too far ahead of ourselves. Just focus on playing good baseball. But it is real exciting being at home down the stretch, and in the driver's seat."
Holliday left the contest in the sixth inning after he was hit on the funny bone of the left elbow by a pitch from Christian Garcia. He is listed as day to day.
"Everything came back negative," Matheny said. "He got hit in a bad spot. I don't care if you hit it on the counter at home, that's a bad spot."
St. Louis will send Kyle Lohse (16-3, 2.77 ERA) to the mound Saturday against Jordan Zimmermann (12-8, 2.90) in the middle game of the three-game set.