After a promising start, the Sea Eagles fell away for a 24-6 loss in their Saturday night clash at AAMI Park but that was no fault of Garrick, who shifted from the centres to cover loss of Tom Trbojevic.
During Wednesday's State of Origin, luckless Trbojevic ruptured his pectoral muscle and will undergo surgery on Tuesday with his season over.
While Roger Tuivasa-Sheck, who is returning to the NRL from rugby union next season, was in Manly's sights as an injury replacement, coach Anthony Seibold said he was "unavailable".
Against Melbourne, Garrick showed some defensive starch while he also ran for 177m as he tried to spark the Manly attack.
He won praise from Seibold, who declared he would play at No.1 going forward.
"I thought he was outstanding - his effort off the footy - he made a try-saving tackle on Xavier (Coates) and then he came across on Will Warbrick there," Seibold said.
"He (Warbrick) got the ball away for their first try but just some of his efforts off the ball were outstanding so I think Reuben will have that No.1 going forward for the rest of the season and we can build some combinations and cohesion.
"He's really only had one or two training sessions there and that was without Chez (Daly Cherry-Evans) so he will be better but I really liked his start there."
Due to inconsistent form, Manly remain outside the eight, sitting 12th, with second-half errors cruelling their chances against Melbourne.
Seibold said he couldn't blame the defeat on changes to their spine.
"You'd like to think we're better than that," he said.
"We made some errors on tackle two and when we had some opportunities in the second half on tryline attack we didn't look on song."
While Manly have lost Tom Trbojevic, his brothers Jake and Ben will return from injury next week as will winger Jason Saab and centre Brad Parker.
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