He has been getting big hit after big hit ever since he came over from Detroit before the July 31 trade deadline.
But as he pointed out, the quest for a championship is only just beginning for the Diamondbacks.
"This isn't it," Martinez said. "They only get bigger from here. In my opinion, we are not in the playoffs yet. If we win that wild card, then we are in it."
Martinez lined a two-out RBI single to deep left field with the bases loaded in the ninth inning, and Arizona beat the Miami Marlins 3-2 on Sunday to clinch the top wild card in the National League.
"J.D.'s been unbelievable," first-year manager Torey Lovullo said. "How fitting that the guy you pick up in a big midseason push gets the big hit today. It makes everything very special."
The Diamondbacks, who won only 69 games a year ago but are 90-66 this season, were assured a playoff berth earlier in the day, when St. Louis lost at Pittsburgh and Milwaukee was beaten at home by the Chicago Cubs.
The comeback victory over Miami ensured that Arizona will host the NL wild-card game on Oct. 4. The Diamondbacks think they're ready for the tension of that elimination game.
"It's one thing I'm going to keep saying: We just really get along, man," said Archie Bradley, the bearded late-inning reliever and free spirit who has become a fan favorite. "We really do care for each other. We really do believe in each other. Something special's going on here."
After drenching each other and anyone else nearby with champagne in the clubhouse, the players donned their postseason T-shirts and made the trek across the field to take a dip in the Chase Field swimming pool.
"What a fun way to win it, on a walk-off," pitcher Patrick Corbin said. "All the hard work. It's such a long year. There's so many hours dedicated for this. It's just special. We want to keep this going. We want to have this feeling five more times or something."
Fernando Rodney (5-4) pitched a perfect inning for the win.
A throwing error by reliever Justin Nicolino (2-3) on Kristopher Negron's sacrifice bunt helped load the bases with no outs in the Arizona ninth. Ketel Marte and Paul Goldschmidt each hit into a forceout at home. That brought up Martinez, who has been spectacular since joining the Diamondbacks. He sent Javy Guerra's pitch on a line shot over the head of left fielder Marcell Ozuna to win it.
Chris Herrmann homered for the Diamondbacks
Arizona tied it 2-all when Goldschmidt led off the seventh with a single, went to second on Ozuna's error and scored on Daniel Descalso's single.
"Torey's done a great job with his staff over there," Marlins manager Don Mattingly said. "They play good baseball. They're a tough club."
Miami starter Dan Straily gave up one run and four hits in six innings, striking out nine and walking three.
"He threw a good game," Mattingly said. "Obviously, that's a very good lineup over there, and this ballpark, to keep those guys to one run is a feat."
Corbin allowed two runs and five hits in 6 2/3 innings.
The Diamondbacks learned they had clinched a postseason spot halfway through the fourth inning, with an announcement on the big message board that was followed by a roar from the crowd. In the Arizona dugout, there were hugs and high-fives, and players came out briefly to cheer the fans.
It's the sixth time Arizona has advanced to the postseason in its 20-year history. The other years were 1999, 2001 (World Series champions), 2002, 2007 and 2011.
Plate umpire Jeff Kellogg was hit in the head inadvertently by Marte's bat. After one more batter to lead off the eighth, Kellogg left the game and was replaced at home by first base ump James Hoye.
Diamondbacks: Lovullo said an X-ray on Friday revealed that the fracture in INF Chris Owings' middle finger is not completely healed. The earliest possible return for Owings would be the NL Division Series. ... C Jeff Mathis (broken hand) has been cleared for more baseball activity and hopes he can play in the final series of the regular season at Kansas City.
Check out some of the nastiest pitches that stunned batters in the box including Adam Wainwright's curveball and Jordan Hicks' fastball.
Wei-Yin Chen will make his final home start of the season Friday in a year in which he has been dominant at Marlins Park.
The Tampa Bay Rays have even less room for error to keep their postseason hopes alive after dropping the opener of a four-game series against the Toronto Blue Jays in shocking fashion Thursday night in Toronto.
Angels catcher Francisco Arcia becomes the first player in MLB history to catch, take the mound and hit a home run in Los Angeles' 21-3 defeat in Oakland.
The American League East race is officially over and the New York Yankees can turn their focus toward more pressing matters.
The Red Sox celebrate their third-straight division title with a party in their locker room at Yankee Stadium.