Nicknamed "Lefty", he was originally signed by the Chicago Cubs in 1961 and was traded to the Cardinals on April 7, 1965, with Bobby Pfeil for Bob Humphreys.
He made his big league debut on April 14, 1968, against the team with which he had originally signed, the Cubs. Ernie Banks was the first batter Gilson ever faced — Banks reached base on an error. Overall, Gilson allowed a hit and walked one in two innings in his big league debut, but did not give up a single run. Overall with the Cardinals in 1968, he posted a 4.57 ERA in 13 games.
He was traded along with Dick Simpson from the Cardinals to the Astros for Ron Davis before the trade deadline on June 15, 1968.[1] He played in only two games with the Astros, posting an ERA of 7.36.
Overall, Gilson posted an 0–2 record in 15 big league games. In 251⁄3 innings, he allowed 34 hits, one home run (to Bob Bailey) 15 runs, 14 earned runs, and 12 walks. He finished 7 games, saved 2 and he struck out 20 batters. His ERA was 4.97.
Although Gilson finished with an unimpressive ERA (especially in 1968, when the league ERA was under 3.00), he started off his career not allowing a single run in his first six appearances. His streak was blown when he allowed five runs in 21⁄3 innings against the Los Angeles Dodgers on May 21.
