Saturday, who never coached at the pro or college level prior to his shock appointment by owner Jim Irsay earlier this month, led the Colts for the third time in the narrow defeat, slipping to a 1-2 record.
But Saturday only used the Colts' first timeout on fourth down with 30 seconds remaining before quarterback Matt Ryan threw an incomplete pass to the left sideline for Parris Campbell on fourth-and-3.
Ryan had scrambled for a run on the second-and-17 of the final drive but dived short of the first-down line, yet the Colts played quickly on third-and-3 with running back Jonathan Taylor bottled up before the timeout was called.
"I thought we had plenty of time," Saturday told reporters. "We had plenty of timeouts, so I wasn't too concerned.
"This wasn't a press for time, we just didn't make enough plays."
Ryan, who admitted he thought he was closer to the first-down line on his run, backed Saturday's decision not to call an earlier timeout.
"I don’t mind the call going with some tempo, trying to get that first and probably bang a timeout after that first," he said.
"We didn’t get it, then have to take that timeout on the fourth down call. Credit to them, they did a good job on jumping inside, we had some in-breaking routes.
"It's disappointing. It really is, I think the effort is good, but our execution just hasn’t been good enough."
Ryan was pressured on 44 per cent of dropbacks, which was the highest in a game this season.
The win means the Colts are 4-7-1 overall and second in the AFC South behind the 7-4 Tennessee Titans.
The Steelers improved to 4-7 but remain last in the AFC North. Rookie Pittsburgh quarterback Kenny Pickett enjoyed his third straight game without a turnover, completing 20 of 28 passes for 174 yards.
"He's getting better every week, he's a competitor, he's smart but there's still a lot of meat on the bone," Steelers head coach Mike Tomlin said about Pickett.
"I've always said he's good enough and we're good enough to win while that happens. We acknowledge he's very much in development."