One made his team’s opening day roster. The other wasn’t in the major leagues until May. But once October came around, Julio Rodríguez of the Seattle Mariners and Michael Harris II of the Atlanta Braves were not only the starting center fielders for their playoff teams, but both also had signed contract extensions that promised to keep them in place into the 2030s.

On Monday, Rodríguez and Harris, both 21, won M.L.B.’s Jackie Robinson Rookie of the Year Awards, which are presented annually by the Baseball Writers’ Association of America.

For Rodríguez, who spoke boldly before the season about his ability to find personal and team success with Seattle, which had not made the playoffs since 2001, the award seemed predestined. He struggled to hit his first month but eventually blasted.284 with an on-base percentage of.345 and 28 home runs.

Mike Trout (2012 Angels) and Chris Young (2007 Diamondbacks) are the other major leaguers that have 25 home runs or 25 stolen bases in a season.

With his big personality and exciting blend of speed and power, Rodríguez was the American League’s rookie of the month in May and June before being named to the All-Star team in July. Rodriguez’s popularity skyrocketed after he hit 81 home runs in three rounds of the Home Run Derby. He lost in the finals against Juan Soto.

“It’s like a dream,” Rodríguez told reporters after his All-Star selection. “It’s like a dream that I had as a kid, and being able to receive that right now, in my first year, I’m definitely excited about the work that I’ve done.”

The accolades continued, and the Mariners placed an enormous bet on Rodríguez’s future in August by agreeing to a massive (and complicated) contract extension that guarantees him $210 million over 12 years but could be worth up to $470 million if he hits certain benchmarks.

Rodríguez’s charmed season culminated with the Mariners snapping their 20-season playoff drought, which was the longest in the major men’s American team sports leagues. The Seattle Mariners beat the Toronto Blue Jays, but lost to Houston Astros in the division series.

With 29 of 30 first-place votes, Rodríguez held off the A.L.’s other two finalists, catcher Adley Rutschman of the Baltimore Orioles and outfielder Steven Kwan of the Cleveland Guardians, as well as Astros shortstop Jeremy Peña, who was not a finalist for his work in the regular season — he finished fifth behind the three finalists and Kansas City’s Bobby Witt Jr. — but who was the most valuable player of the American League Championship Series and the World Series.

Harris, a third-round pick in 2019, did not arrive with the same hype as Rodríguez — ranked him as the 65th-best prospect in the minor leagues before the season — but he continued a long tradition of Atlanta’s finding gems in its own backyard: He once starred at Stockbridge High School, about 40 miles south of Truist Park in suburban Atlanta.

Harris was promoted from the minors after batting.305 and an impressive slugging percentage of.878 during the first two seasons at Class A Mississippi. He proved he could help the team with his bat, legs and glove: He was the National League’s rookie of the month in June, August and September.

Harris managed to hit.297 in 114 games. He also stole 20 bases, scored 75 runs and had 19 home runs. According to Baseball Reference, Harris tied for fourth in defensive wins above replacement, but played far fewer games than those who came before him.

Atlanta continued its recent trend of aggressively seeking long-term deals for its young stars. In August, Harris was signed to an eight-year extension worth $72 million. He will be under contract until 2030, with club options for 2031 or 2032.

With 22 of 30 first-place votes, Harris held off the N.L.’s other two finalists: his Atlanta teammate Spencer Strider, a right-handed starting pitcher who also signed a lengthy contract extension with the team, and Brendan Donovan, a utility player for the St. Louis Cardinals.

The Awards season will continue with the Manager of the Year Awards this Tuesday, the Cy Young Awards next Wednesday, and the Most Valuable Player Awards next Thursday.