West Ham signed Haller from Eintracht Frankfurt in July 2019 for a reported club record fee of 45 million pounds ($58.08 million) but the 26-year-old managed only seven league goals in his first season.
"It was great that Seb scored a couple of goals, it really is, because we need our forward players to be feeling confident about it. The two goals tonight I'm sure will help him," Moyes told reporters.
"We had Michail Antonio scoring for us at the end of last season and now we hope Seb gets on a run of scoring goals."
Moyes said midfielder Jack Wilshere, who has been linked with a move away from the club, missed the match due to an ankle problem.
West Ham will take on Leeds United or Hull City in the next round of the competition next week and travel to Arsenal in the Premier League on Saturday.
($1 = 0.7748 pounds) (Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Peter Rutherford )