Now the two of them have emerged as the core of their club's offense. Upton is an All-Star right fielder, and at 22, has all kinds of potential. Reynolds, now a 26-year-old third baseman, hit 44 homers last year. The club locked them in this spring, signing Upton to a six-year, $51.25 million contract and Reynolds to a three-year deal for $14.5 million.
They have had to develop and learn baseball's hard lessons in the Major Leagues. And as manager A.J. Hinch, all of 35 himself, said: "They're not kids anymore."
"They've already come of age," Hinch said. "They're maturing every day and they're learning at this level. They've had to learn at this level, but they've been here long enough. They're bona fide Major League players with great futures ahead of them. [They] have come into the season with a little bit of an edge."
Upton was 2-for-4 in the opener, scored two runs and was on base three times. Reynolds launched his first homer of the season with two out in the third inning, a two-run shot off a Jon Garland hanging curveball. He also walked twice and whiffed once in the game.
After Stephen Drew's rare Opening Day inside-the-park homer, the D-backs led, 6-0, and had the game well in hand in the fourth inning. That's the game plan, Upton said. Score early and bury the opposition.
"We want to beat the other team, we want to make them submit," Upton said. "We don't want it to be a game at the end. We don't want it to be close. Obviously, every game can't be like that. But when we get ahead, we want to stay ahead."
The pair has had trials and tribulations. In 2008, Upton slumped and was sent back to Triple-A for 15 games. Last year, he was benched when he misjudged the length of a shot to center field at Coors Field. Thinking that it was a homer, he trotted down to first base. When the ball hit the fence he had to settle for a single.
Reynolds has whiffed 557 times in three seasons, setting a Major League record in 2008 with 204 and then shattering that mark last season with 223 when he also had the 44 homers and 102 RBIs.
Mays, at 20, batted .274 with 20 homers and 68 RBIs in his Rookie of the Year 1951 season for the New York Giants. But he slumped late in the season and batted .182 (4-for-22) with no homers and an RBI in the Giants' World Series loss that fall to the Yankees. Mays wasn't to blossom until after he spent almost two years in the service and came back as a 23-year-old in '54, when the Giants won the World Series and he led the National League with a .345 batting average, adding 41 homers and 110 RBIs.
Mays had self doubt and suffered through some criticism -- just like Reynolds and Upton. Both players came up in 2007 when the D-backs won the NL West title and were swept by Colorado in the Championship Series. Reynolds batted .176 (2-for-16) with a homer and an RBI in that series, Upton batted .222 (2-for-9) with no homers or RBIs.
"We both kind of got thrown into the fire," Reynolds said. "We've obviously had our downs. We had a lot of people riding us, a lot of people saying we weren't going to amount to anything. We just grew and got better with experience. J.U. is an All-Star and I'm doing my thing. I hope we can just keep it going for many years to come."
"I really didn't see it being a problem," Upton said. "Each year I didn't know how much better I could get until I went through it. There were ups and down, but these are things you just don't worry about. You just go out and play. You can learn something new every day."
Mays, of course, played 22 years and is a member of the Hall of Fame. He never won another World Series and only played in it two more times ('62 and '73). For Reynolds and Upton, the world is still ahead of them, but the jury is still out.