ST. LOUIS -- Upon learning that he would make his postseason debut in Game 1 of the National League Division Series, Gio Gonzalez recalled his mind becoming a carnival of "back flips" and "cartwheels" and "excitement."

As if the assignment could have gone to anybody else.

"It was really an easy choice," Nationals manager Davey Johnson said. "Gio would have hung me if I didn't have him going first."

Wild Card vs. Nationals

And so, fresh off his Cy Young-caliber debut season in Washington, Gonzalez will start Game 1 Sunday at 3 p.m. ET on TBS. The Nationals hope only that he will be able to channel all that eagerness and intensity into a successful outing against the Cardinals at Busch Stadium.

There is plenty of reason to believe that he will. Visibly loose and lighthearted on the eve of his postseason debut, joking about the weather and his haircut, Gonzalez seemed every bit as relaxed as the pitcher who lost just once in his final six regular-season outings. The lefty posted a 1.35 ERA over that span to make a serious run at the National League Cy Young Award.

He may not boast as much big-game experience as some of his teammates, and certainly not as much as his defending champ opponents, but Gonzalez has pitched in front of packed houses before. He has also developed into one of the most consistent starters in baseball over the past three seasons, improving his control this summer to make the leap from Very Good Pitcher to Bona Fide Ace.

Which is convenient, because midway through their season, the Nationals found themselves in need of one.

They once had an ace in Stephen Strasburg, but shut him down on an innings limit. They leaned heavily on Jordan Zimmermann early in the year, but watched him struggle in August and September.

That left Gonzalez, to whom even Cardinals manager Mike Matheny offered his profound respect.

"He's good," Matheny said. "I mean, there's no getting around it."

The Nationals, of course, knew they were receiving a good pitcher when they acquired Gonzalez from the A's last winter for Derek Norris, Tommy Milone, A.J. Cole and Brad Peacock, in a trade that has since benefited both clubs immensely.

At first, Johnson was not entirely sold on the South Florida lefty, whose ceiling seemed limited by his lack of command. But Gonzalez thrived under new pitching coach Steve McCatty, improving on just about every statistical category imaginable. He threw more strikes. He walked fewer batters. He struck out more hitters. He allowed fewer home runs.

And he won more -- and more, and more, and still some more, leading the Majors with 21 victories. Gonzalez credited his offense for that, recalling one August start in which the Nats plated 14 runs for him. Indeed, only Lance Lynn of the Cardinals received more support than the 5.38 runs the Nationals averaged in Gonzalez's starts, making the left-hander's improvement all the more potent.

But if that trend is to cease, it will do so in October, when runs are almost always at a premium. It will then be Gonzalez's job to rely not on his offense, but on himself.

"I'm not in any way, shape or form trying to show any signs of weakness," the left-hander said. "I'm just too excited about it. I mean, first time ever to experience something like this, and to do it against a team that won the World Series last year, it's a privilege."

As for those defending-champion Cardinals, Gonzalez faced them only once this season, firing a five-hit shutout Aug. 31 at Nationals Park. Thanks in large part to the statistics he accumulated that day, Gonzalez has held the 25 players on St. Louis' playoff roster to a combined .161 lifetime average with just one extra-base hit in 31 at-bats. The Cards' five most-feared sluggers -- Carlos Beltran, Matt Holliday, Yadier Molina, Allen Craig and David Freese, who accounted for 77 percent of the team's home runs this season -- are a combined 1-for-15 against him.

Translating those regular-season accomplishments into NLDS Game 1 will be the next challenge for Gonzalez, who hopes his inaugural postseason start can be every bit as successful as his first summer in the District.

"It's a childhood dream," he said. "I think it's every kid's childhood dream who wants to play baseball. There are so many things that factor into this that you take it with a smile."

"Gio has the same temperament no matter how big the game is," said Johnson, whom Gonzalez, fittingly, once accused of not smiling enough. "He just enjoys going out there and expressing his talent."