The South African winger returned to Everton on loan for the rest of the season last week, just 12 months after leaving for Tottenham
The former Ajax player enjoyed a successful three-year stint on Merseyside after his career stalled at Borussia Dortmund.
He was outstanding in the 1-1 draw at Wigan and looked likely to create plenty of chances alongside Landon Donovan, who is on loan from LA Galaxy, in midfield.
Everton have struggled for goals this season but Moyes is sure that Pienaar, 29, will have a major impact in the second half of the season.
"Steven Pienaar was the best Everton player. He came back and looked as if he hadn't been away," Moyes said.
"He was involved in a lot of bits where we looked as if we were on the verge of making things happen but things just broke down around the edge of the box but Steven Pienaar played really well."
The Everton manager only gave Nikica Jelavic, who also joined on transfer deadline day in a £5.5 million move from Rangers, a 30-minute run-out.
But he is also satisfied with the early days of the Croatian striker's Everton career.
"He did fine. He's only just come into it so it's difficult to judge," he said. "He only really joined us on Friday and we'll give him a chance to settle in and be part of it."
Everton lost Australian midfielder Tim Cahill to a foot problem at half-time at the DW Stadium.
Moyes revealed that Cahill is also struggling with a calf problem but is not sure how long he will be sidelined.
"Tim Cahill got a foot injury in the first half early on and I was going to sub him but I was hoped that I could get him through but he had to come off at half time," he said. "He's got a bit of a foot problem and a calf as well."
Wigan looked set for just a fourth victory of the season when they took the lead through a Phil Neville own goal in the closing stages at the DW Stadium.
But Victor Anichebe headed in just three minutes after coming off the bench to earn Everton a point.
Chilean winger Jean Beausejour arrived at Wigan from Birmingham in the run up to the transfer deadline and his new manager Roberto Martinez believes his new signing has already made a difference.
"Jean is settling in really well. He's a specialist in the position that he plays and he's been a real boost to the squad. It will take time to get the real benefit of his quality," Martinez said.
"He can find a cross when maybe you don't expect that and we have to understand his real quality but it was pleasing to see such a natural home debut from Jean.
"It seemed like he's been playing for us for a long time. He's a great character and fitting in well with what we're trying to do."
Wigan, who are bottom of the Premier League, are now five points from safety but Martinez is still certain that they will manage to avoid relegation.
"The situation that we've been in the table affected us in the last two games but that wasn't the case against Everton," he said.
"It was a free group that really enjoyed getting on the ball and working hard for each other and that gives me great confidence to look forward to the end of the season.
"We've been in this situation before and we know that it's going to be extremely difficult but we are a strong unit and that's the challenge that we've got ahead."
Source: AFP
Source: AFP