The match went to three sets and by the time Tamai won the third in a tiebreaker the pair had been battling away for more than three hours.
Rotorua's Sean Martin, James Wilce and Jesse Galvin-Dawson were also in great touch to win their singles matches as the local club progressed to their second successive final.
Captain Tamai said he was rapt with how his team played once again this season. He said the support, in particular, was helpful.
"It is great support, all these guys ... this is what it is all about," he said. "It is great playing in front of family and gives us that extra bit of oomph."
He said his match with Merchant was a marathon and showed how much character his opponent had.
"That young guy was brilliant, even though they had lost the match he fought all the way. He could have easily said 'stuff it' and given up, but he had a great heart."
Tamai said they would be prepared to play either club, Lugton Park or Whakatane, in the final but preferred the latter.
"Both will be tough but, at the end of the day, it would be great to have two Bay of Plenty teams in the finals. Same as last year with Otumoetai, it would be good for the Bay."
Lugton Park and Whakatane play their semifinal this coming Saturday in Whakatane after their match was postponed.
