Grant Jackson.
Jackson came into the game with two outs in the 5th inning and the score 1-0 in favor of the Orioles. He pitched 2 2/3 innings, leaving the game with one out in the 8th inning and the Pirates ahead, 2-1.
Using the current definition of an MLB rookie, an educated guess would be Babe Adams of the 1909 Pittsburgh Pirates.
Adams had pitched 26 MLB innings prior to the 1909 season and current MLB rookie rules state a pitcher is a rookie until pitching 50 innings. Current rules also state a player cannot have been on a team's active roster for more than 45 days during the time of a 25 player roster. This time does not include the month of September when rosters are allowed to be expanded to include callups from the minors. I don't know how long Adams was on the Pirates active roster, so that's why I said an 'educated guess'.
Adams pitched three complete games (Games 1, 5, and 7) in the 1909 Series and won all three, pitching to an ERA of 1.33.
Through the 2009 World Series, John Lackey of the 2002 Angels is the only other rookie to have won a Game 7.
It was Joe Wood in 1912 who beat Christy Mathewson for the NY Giants in the 10th inning of game 7.
Jack Morris was the winning pitcher in game 7, of the 1991 World Series.
Derek Jeter won his first World Series in his rookie year, 1996.
In Game 1 of the 1996 World Series, rookie Andruw Jones of the Atlanta Braves hit home runs in his first two at bats.
Babe Adams of the 1909 Pittsburgh Pirates who pitched a complete game against the Detroit Tigers in Game 7, winning 8-0. Adams had an outstanding rookie season going 12-3 with a 1.11 ERA in the regular season and 3-0 with a 1.33 ERA in the World Series. All three of his wins in the WS were complete games.
The first World Series MVP award was given out in 1955. It was won by Brooklyn Dodgers pitcher, Johnny Podres.
Burleigh Grimes
The first left-handed pitcher to achieve three wins in one World Series was John Tudor of the St. Louis Cardinals in the 1985 World Series against the Kansas City Royals. Tudor won Games 1, 4, and 7 of the series.
Old-time pitcher Pud Galvin had 364 lifetime wins, but his career ended 11 years before the first World Series game was ever played.
Babe Ruth for the Boston Red Sox in Game 5 of the 1918 World Series against the Chicago Cubs ... he was the starting pitcher and batted 6th.
5 - Derek Jeter was a rookie when he first won.
Jim Bagby of the Cleveland Indians hit the first home run by a pitcher in Game 5 of the 1920 World Series.
1920
Ron darling