Mata’utia, 27, joined from financially-crippled Leigh Centurions last week and immediately proved his worth with an impressive showing in yesterday’s 52-24 win at Widnes Vikings.
Although signed as a full-back, he started at centre and showed plenty of class before limping off midway through the second period with cramp.
Powell said: “I thought he was excellent.
“He was strong in the centre, beat people, has got a good offload and a right foot step that’s really strong.
“He just looks like he’s difficult to handle – he got us moving with some fast ruck speed – and I think he’ll be a really good signing for us.”
But Powell also praised Mata’utia’s fellow Samoa international Quentin Laulu Togaga’e who retained the full-back role and scored two tries during the rout.
“I thought Q was great,” he said.
“He had a tough message during the week – we got Pete in, another full-back – but he handled it really well, very mature, and went really well today.”
Slow-starting Castleford initially trailed 12-4 but turned on the style with four back-to-back tries in just seven minutes to leave bottom-placed Widnes destined for a 16th successive Super League loss.
“We didn’t start great and didn’t finish great but in between I thought there was some outstanding rugby league played,” said Powell.
“I was really pleased. For us to finish third after the regular rounds after what’s happened to us this year is an outstanding effort from the boys. They have four days off now and deserve a few beers.”
Widnes boss Francis Cummins said: “There was a 10 minute spell when we just didn’t touch the ball.
“You could see Cas’ quality them but we have to be better than that.
“Fortunately we’re not playing them every week (in the Qualifiers).”