Fifth in a series examining the Red Sox roster for 2018

The Red Sox opened last season with Pablo Sandoval at third base. He was in the third year of a five-year, $95 million contract that will be remembered as one of the worst in baseball history.

Sandoval failed to hold his spot and was released in July with $47.8 million left on his deal, virtually all of which the Red Sox will have to pay off. Their return investment was 161 games and a .646 OPS.

But by the time the season had ended, third base represented a position of hope, if not strength, for the Red Sox with the ascension of Rafael Devers.

Devers played only nine games in Triple A before making his major league debut on July 25 at age 20. The lefthanded hitter played in 58 games and hit .284 with an .819 OPS. Devers had 24 extra-base hits and 30 RBIs.

Devers joined Ted Williams and Tony Conigliaro as the only Sox players to hit multiple home runs in a game before the age of 21.

Devers also became the first player in history to hit eight home runs in his first 20 games before the age of 21.

He hit well at Fenway Park (.312), against lefties (.400), with runners in scoring position (.296), and against the Yankees (.306).

Devers was 4 for 11 in the Division Series against Houston and homered twice. He has uncommon power, particularly to the opposite field, for a player his age and quick hands that enable him to make good contact on pitches many hitters would take or at best hope to foul off.

But there are issues. Devers committed 14 errors in 56 games at third base and will need a daily dose of work in spring training to smooth out his deficiencies in the field. His throwing is a particular concern.

For new infield instructor Carlos Febles, getting Devers ready should be a priority. That Febles managed Devers in Double A Portland will ease that transition. New manager Alex Cora, a former infielder, should be a tremendous benefit to Devers as well.

Devers, who turned 21 last month, also needs to work on his conditioning or risk losing the athleticism needed to play third base. Devers has far greater value to the Sox (and his future earnings potential) as a third baseman than he does as a first baseman or DH. The Sox would be wise to get Devers signed up with a high-end training center before he reports to spring training. That path benefited Xander Bogaerts early in his career.

Ideally, the Sox would get 150 or so games out of Devers and reap the benefits of high production at a low cost. That would somewhat ease the sting of paying Sandoval to play for the San Francisco Giants.

There is ample depth at third base. In Marco Hernandez, Brock Holt, Tzu-Wei Lin, and Deven Marrero, the Sox have four players with experience at the position.

Lin and Marrero gave the team a lift in June and July, bridging the gap from Sandoval to Devers. Holt has been a reliable backup for four seasons now, but has hit only .237 the last two.

Were it not for Devers, Hernandez could be the third baseman of the future. The 25-year-old has shown potential at the plate in 61 major league games. The immediate plans are for him to play second base while Dustin Pedroia recovers from knee surgery.

There are two third basemen with power in the minors who may have to change positions, as both are older than Devers.

Michael Chavis, 22, had a .910 OPS and 31 home runs in 126 games for Single A Salem and Double A Portland. He followed that up with 23 more games in the Arizona Fall League. Chavis had an .805 OPS in those games and four more home runs. He also played first base for the first time in his professional career.

Chavis struggled at the plate before last season, so 2018 will help determine how viable a prospect the former first-round draft pick is.

Bobby Dalbec, 22, was a fourth-round pick in 2016 from Arizona. He has 20 home runs in 119 professional games, all in Single A. He is likely to open next season in Salem.

Dalbec has so far only played third base with some games as the DH. If Devers becomes established at third base, a positional change could be made down the road.

Third base

Primary 2017 starter: Rafael Devers.

Projected 2018 starter: Devers.

Major league depth: Marco Hernandez, Brock Holt, Tzu-Wei Lin, Deven Marrero.

Prospects to watch: Michael Chavis, Bobby Dalbec.

Peter Abraham can be reached at pabraham@globe.com.