Both fighters supreme conditioning saw them last the full four rounds, with Gallen resembling an immovable object while Thompson continually tested him with a range of powerful shots and evasive footwork.
"I knew it was going to be tough," Gallen said.
"We were never going to knock each other out, he was hard to hit and he kept coming."
In the heavyweight title fight, Auckland's Hemi Ahio made short work of All-Samoan champion Alipati A'asa, dispatching him in two rounds with a brutal display of power hitting.
The underrated A'asa looked to be headed for an upset victory after a strong start, but Ahio's heavy hands soon took their toll. He knocked his rival down twice in the second round with a pair of left and rights to take the win.
Earlier, reigning Super 8 cruiserweight king Israel Adesanya retained his crown after easing past Zane Hopman in the knockout tournament semi-final, before claiming his second unanimous decision victory of the night in the final over the hard-hitting Lance Bryant.
Adesanya's effort was all the more remarkable for the fact he was backing up just three days after winning the trans-Tasman King in the Ring, in which he won past three opponents.
The light heavyweight knockout tournament final, between recent world title challenger and NZPBA champion Robert Berridge and New Zealand NZPBF titleholder Reece Papuni, was a ruggedly fought crowd pleaser.
Both fighters arrived after surviving their respective semifinal bouts, which were both forced into a fourth deciding round, with Papuni seeing off Bradley Riddel and Berridge accounting for Sosefo Falekaono.
The super-fast Papuni looked the more dynamic and powerful but Berridge was tough enough to take it to three rounds before the pair engaged in a fourth, with Papuni eventually declared the victor by split decision.
In between the two knockout tournament finals, former Shortland Street star Bree Peters take a unanimous decision victory over Bachelor NZ contestant Lisa O'Loughlin.
