The Warriors held off a couple of Tigers' fightbacks on Saturday night, Vatuvei's second try giving them breathing space with 10 minutes to go.
Pat Richards' try five minutes later brought the Tigers back to within four points before second-rower Bodene Thompson sealed victory with a four-pointer with 80 seconds to go.
"(Vatuvei's milestone match) definitely played a part in it," Mannering said.
"I'm sure Manu wanted us to concentrate on the result, but it was such a special occasion for him.
"He's so much about this club and team that it wouldn't have been fair if we didn't get the result tonight."
Vatuvei's two tries took him to 140 for his career and level with Nigel Vagana as the most-prolific New Zealand try-scorer in NRL history.
The result at Mt Smart Stadium left both clubs with 3-3 records, but with the Tigers slightly better on for and against.
It was the visitors who struck first through the first of centre Tim Simona's two tries.
From there, the Warriors dominated.
They sent plenty of the play to Vatuvei's edge and he obliged by getting them on the board in typical fashion, powering past two tacklers.
After five-eighth Chad Townsend, fullback Tuimoala Lolohea and halfback Shaun Johnson also scored, it looked like the Tigers, who had both the possession and penalty count against them, would be left behind.
But from a rare attack, fullback James Tedesco crossed to help close the gap to 20-12 at halftime.
Simona then produced a double fend on Hurrell and Johnson to complete his brace.
Richards' third conversion made it a two-point ball game, before Vatuvei got his second try to open out the gap.
While Tigers coach Jason Taylor was disappointed with the defeat, he praised his players for the way they hung in.
"(The Warriors) are big and strong and they run the ball really hard and they tested us," he said.
"I was really impressed with the way we fought back and never gave up.
"They were the better team probably for a longer period than us, but only just."
Tigers prop Aaron Woods finished with a match-high 195 running metres, but was also put on report for a late hit on Townsend.
