Pulisic, 22, has played 84 minutes out of a possible 450 in the Premier League under Tuchel, who replaced Frank Lampard as coach on Jan. 26.
"Well today the first change was already made in the first half from injury and Christian was a tight decision on whether he starts again after the Cup game, or if he comes from the bench and another 11 starts," Tuchel said after Chelsea beat Newcastle United 2-0 on Monday.
"Unfortunately we only have three changes which makes it very, very difficult to give time to the players to play what they deserve and to have an impact. It makes it difficult as the third change, you don't want to use that too early.
"So we did what we always do the middle of the match we only think about what can help you win the match.
"Christian absolutely deserved to start, he deserved to come in, so I hope he keeps on going and I'm absolutely sure he will be an important influence for us and make an important impact for us in the future."
After an impressive first season in the Premier League last year, injuries have hampered Pulisic's involvement this term. He has scored twice in all competitions during the 2020-21 season.
He also missed the game against Sheffield United on Feb. 7 due to a family issue.