Early in the second spell Rovers had a reasonable appeal for a penalty turned down and that proved to be the decisive point of the game.
Lamb then scored to increase the visitors' lead and took his tally to four with two penalties.
Claudelands scored a late consolation goal but had to hand over the shield at the end of the game.
It was another frustrating day for Rotorua United coach Neil Rush against Otumoetai.
After an even opening quarter, Laurie Scott gave United the lead, which they held until the break. And while they dominated early in the second half, they could not increase their advantage.
Otumoetai gradually got back into the game and in the 70th minute Matt Fisher scored to tie the game up.
With 10 minutes left, Otumoetai were unlucky when a rocket of a shot beat United goalkeeper Andrew Gibbs but struck the inside of the post. However, within seconds, they went ahead through Matt Collins.
Then after United's Niki Te Miha was denied by a great reflex save from keeper Graeme Blisset, Otumoetai closed the game out with a Tim Miller goal for a 3-1 win.
And United coach Rush could only contemplate what could have been.
At Stembridge Rd AFC Fury were convincing 3-0 winners over an under-strength Ngongotaha.
The Villagers' coach Shane Davis acknowledged Fury deserved their win.
"They are a good side and we never got into the game," he said.
It's a small pitch at Southey Park but the Old Blues versus Tauranga Boys' College had plenty of quality football.
The college side had a 1-0 lead at the break but Old Blues coach Andy Legget re-jigged his formation for the second half and a double from Andy Cooper and a goal from Hayden Fowke saw them run out 3-1 winners.
Melville United bounced back from last week's 7-1 loss to Taupo to beat Otorohanga 7-0 at Gower Park while Waikato Unicol beat Whakatane Town 2-0.
In division two, leaders Tauranga City had a 2-0 win over Te Awamutu at Links Ave while Cambridge kept their challenge alive with a narrow 1-0 win at home against Katikati.
Tokoroa scored the only goal to beat West Hamilton 1-0, and Rotorua United beat Matamata 3-1.