The Coasters got together for Heartland's reply try as Lash held up his pass after a 5m scrum and maul, before hitting West Coast second-five Sione Holani in the gap for a converted try to close the margin to 15-14 at the break.
Samoa drove from an attacking lineout to put their lock Kane Leaupepe over from the back of the maul, with Tusi Pisi taking over the goal kicking to put them eight points ahead.
It was provincial neighbours combining again for Heartland's third try as Wanganui's reserve halfback Lindsay Horrocks fired a cut-out pass to his second-five Peni Nabainivalu, who put Horowhenua-Kapiti winger Willie Paia'aua free down the tramlines to score for 22-19, with Lash hitting the posts from his sideline conversion.
Clare and Thames Valley winger Harry Lafiuanei dashed back to stop Samoa scoring off a grubber kick to the in-goal, but under pressure, the New Zealand team lost their North Otago lock Josh Clark to the sinbin for a professional foul, seeing the islanders drive again from the lineout for Ala'alatoa to get a double.
At 29-19 entering the final quarter, play became end-to-end stuff, as Wanganui's import to Horowhenua Kapiti in Timoci Seruwalu came on to make a great cover tackle to force a turnover, while Clare tried an audacious chip kick and regather from his 22m, which he then kicked ahead again towards Samoa's tryline.
However, Samoa turned on some razzle-dazzle of their own to run back out to halfway, and then a perfect cross kick was collected by Tuala, who could have got a hat trick but causally gave the ball to second-five Rey Lee-Lo to score on fulltime.
Heartland XV coach Mark Rutene said his players loved the experience of playing an international on the home ground of New Zealand rugby.
He pointed out that aside from the opening Mitre 10 Heartland Championship round and some preseason rep matches, the squad had basically come out of rural club rugby before the clash.
West Coast captain Troy Tauwhare had led the team in a proud haka before kickoff.
Samoa 36 (Michael Alaalatoa 2, Ahsee Tuala 2, Kane Leaupepe, Rey Lee-Lo tries; Tusi Pisi 3 con) bt NZ Heartland XV 19 (William Wright, Sione Holani, Willie Paia'aua tries; James Lash 2 con). HT: 15-14.