The Phillies agreed to a five-year, $118 million contract with free-agent pitcher Zack Wheeler on Wednesday, a source told MLB.com. The club has not yet confirmed the deal, but when it becomes official, it will be the second largest by total value the team has ever given to a free-agent pitcher, behind Cliff Lee’s $120 million deal before the 2011 season.

But Wheeler’s contract is particularly notable because of his résumé. One of the most intriguing parts of Wheeler’s free-agent candidacy is that his payday is based more on potential than fellow free agents Gerrit Cole and Stephen Strasburg.

Wheeler was the sixth overall pick in the 2009 Draft, and the eighth-ranked prospect entering his debut season in 2013, according to MLB Pipeline. In other words, the expectation of potential has been there since the beginning. That grew even more when Wheeler had a solid rookie season and was good in 2014. But he missed the entire '15 and '16 seasons after undergoing Tommy John surgery, leaving his potential unrealized for little longer.

Wheeler’s 2018 was the best year of his career, and he pitched well this past season, too. Still, his popularity on the market this offseason spoke to the fact that he still appears to have room to grow.

This brings us to the most interesting quirk of Wheeler's contract. Even now, at age 29, he’s only thrown 749 1/3 Major League innings -- the fewest of any pitcher prior to signing a $100 million free-agent contract. That excludes pitchers who signed big extensions early in their careers (such as Strasburg), as well as Masahiro Tanaka, who signed directly from Japan after an established career there. Yu Darvish also had thrown 832 1/3 Major League innings before he signed with the Cubs in 2018, but he had thrown over 1,000 innings in Japan first.

Here is a look at the five pitchers prior to Wheeler with the fewest career innings under their belts before landing nine-figure free-agent contracts.

Patrick Corbin: 945 2/3 IP -- 6 years, $137.5 million from Nationals

How he got the deal: Corbin first made an All-Star team as a 23-year-old in 2013 with the D-backs. From there, he missed the entire '14 season after having Tommy John surgery, and he didn’t quite find his form again ... until '18, his final year before free agency. It was good timing, as Corbin struck out a career-high 246 batters, had a 3.15 ERA, established his slider as one of the best in the game and showed that his injury woes were perhaps behind him.

How it worked out: It’s only been one season, but Corbin already has a World Series title to his name with the Nationals. His actual performance in 2019 was pretty similar to his contract year: 3.25 ERA, 238 strikeouts. He was a solid number three behind Max Scherzer and Strasburg and he was versatile in the playoffs, making three starts and five relief appearances. His outings were far from perfect, but he pitched a crucial scoreless 1 1/3 innings in NLDS Game 5, got a key ninth-inning out in NLCS Game 2 and had scoreless relief appearances in World Series Games 1 and 7.

Jordan Zimmermann: 1,094 IP -- 5 years, $110 million from Tigers

How he got the deal: Zimmermann pitched seven seasons for the Nationals, posting a sub-3.75 ERA and making at least 25 starts in each of the final five -- after returning from Tommy John surgery. He was an All-Star in 2013 and '14, and received Cy Young Award votes in each of those years as well.

How it worked out: Zimmermann is entering the final year of the deal in 2020, and it hasn’t exactly gone according to plan. After having a 3.32 ERA in those 1,094 career innings with the Nationals, Zimmermann has a 5.61 ERA in 508 2/3 innings with the Tigers. He threw 190-plus innings in each of his last four seasons with the Nats, but he has yet to approach that total with the Tigers -- topping out at 160 in 2017, when he tied for the Major League lead in earned runs with 108.

Max Scherzer: 1,239 1/3 IP -- 7 years, $210 million from Nationals

How he got the deal: Scherzer, a first-round pick by the D-backs in the 2006 Draft, was traded to the Tigers in a three-team deal following the '09 season, after two years at the Major League level with Arizona. He really found his groove from 2012-14 with Detroit, winning the American League Cy Young Award in '13 and finishing in the top five in '14, too, as an impending free agent.

How it worked out: Scherzer has won two Cy Young Awards, thrown two no-hitters and won a World Series with the Nationals. It’s fair to say he’s already been worth the investment -- with two years still left on the deal.

Mike Hampton: 1,260 2/3 IP -- 8 years, $121 million from Rockies

How he got the deal: Hampton debuted as a 20-year-old with the Mariners in 1993, pitching in a handful of games, mainly as a reliever. They traded him to the Astros, who used him in relief in '94. The next year, Hampton became a full-time starter, and from 1995-99, he had a 3.39 ERA in 151 starts for Houston. He finished second to Randy Johnson for the 1999 NL Cy Young Award. Before his contract year, the Astros traded Hampton to the Mets, and he put up a 3.14 ERA while winning a Silver Slugger Award.

How it worked out: Hampton ultimately played just two seasons for the Rockies before he was traded, posting a 5.75 ERA in 62 starts. And lest we blame Coors Field, he had a 5.73 ERA at home in that span -- and a 5.77 ERA on the road. Hampton was traded twice in a span of three days in November 2002, first by the Rockies to the Marlins on Nov. 16, then by the Marlins to the Braves on Nov. 18. He remained with the Braves for the rest of the contract but missed two entire seasons after having Tommy John surgery in September 2005.

Cliff Lee: 1,409 IP -- 5 years, $120 million from Phillies

How he got the deal: Lee was a bit of a late bloomer, debuting in 2002 but going through some ups and downs through '07. He then won the '08 AL Cy Young Award with the Indians before getting traded three times between July '09 and July '10. Often, a player changing teams that frequently is an average performer at best, but that was not the case here. From 2008-10, Lee threw 17 complete games, second-most in the Majors behind Hall of Famer Roy Halladay. Despite all that, Lee still had nearly twice as many innings upon reaching free agency as Wheeler did this offseason.

How it worked out: Lee was 32 years old when he signed the contract before the 2011 campaign, and he only managed to pitch four of the five seasons on his deal, suffering an elbow injury in the '14 season and never returning to the Majors. But when he pitched, he was great, with a 2.89 ERA and 1.09 WHIP in 106 starts from 2011-14.