Another exciting piece of the Mariners’ future will soon become the present, as the team announced Wednesday it will select touted prospect Taijuan Walker from Class-AAA Tacoma to start Friday at Houston against the Astros.

It will serve as the much-anticipated MLB debut for the 21-year-old pitcher. The roster move will be made before Friday’s game.

Walker has long been one of the most popular minor-leaguers in the Mariners organization and came into this season as the No. 5 prospect in baseball, according to MLB.com. He has made 25 starts this year for the Rainiers and Class AA Jackson, with a combined 9-10 record, 2.93 earned-run average and 160 strikeouts (tied for fourth among minor leaguers).

Honors this year for Walker — a right-hander who checks in at 6 feet 4, 210 pounds — include pitching in the All-Star Futures Game and being selected as a Southern League All-Star. He will wear No. 27 for Seattle.

In four minor-league seasons, Walker has a 23-26 record, 3.49 ERA and 400 strikeouts. In 11 games with Tacoma, he was 5-3 with a 3.61 ERA and 64 strikeouts.

Walker, at 21 years, 17 days old Friday, will be the fifth-youngest in team history to debut as a starting pitcher.

Felix Hernandez, who took the loss in Wednesday’s 12-4 defeat to Texas, holds that record at 19 years, 118 days.

Seager bomb

There weren’t many highlights from a lopsided loss to the Rangers, but one came in the sixth inning when Kyle Seager blasted a 415-foot home run off the “Hit it Here” Café.

Asked if he’s ever hit one that long, Seager said, “I don’t think I have — not at home anyway. That was a first for me.”

The third baseman tattooed Rangers pitching all year, hitting safely in 18 of 19 games, for a .403 average with 14 runs, 11 doubles, six home runs and 15 RBI.

Joshua Mayers: 206-464-3184 or jmayers@seattletimes.com. On Twitter @joshuamayers.