Tuimavave scored two tries and created another in a man of the match performance, hours after his new four-year contract was confirmed.
“Carlos has been a magnificent signing since the day he came in,” said Last.
“He is a player with a great pedigree and when we brought him in his best years were definitely in front of him.
“He has got comfortable playing in Super League and his level of consistency has been outstanding in all the time he has been with us.
“He is comfortable at half-back and one of the top three or four centres in the competition, in my opinion.”
Tuimavave helped Hull build an 18-6 half-time lead which they extended soon afterwards, before Castleford staged a spirited rally.
Both teams had been in Super League action just three days earlier and Last said: “In terms of quality of performance and composure, it probably wasn’t what I asked for.
“But in terms of character, they showed great desire.
“We had used all our subs with 12 minutes to go and the boys who were out there had to overcome bruises and niggles and to stay honest and keep moving and keep defending the way they did, the players deserve all the credit, along with the medical staff and the strength and conditioning staff.”
Castleford coach Daryl Powell was bitterly disappointed with the result, but “proud” of his team’s effort.
“I thought we were fantastic, the courage we showed,” Powell said afterwards.
“Having been here on Thursday night, the boys didn’t get home until 2am and coming back here on Sunday to play another game in a different competition was always going to be tough. That period just around half-time was the difference out of all of it, they scored an intercept and then straight after half-time from a tap-20. Apart from that, we created some really smart tries. It was a huge, huge effort and we could easily have won that game.”
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