— reporting by AAP

NSW State of Origin coach Michael Maguire will be sweating on the fitness of Haumole Olakau'atu after the Manly forward failed to finish the Sea Eagles' 32-22 loss to Penrith.

Olakau'atu, who made his Blues debut in the opening game of the series, trudged off in the 23rd minute in front of 20,101 spectators at Penrith Stadium on Sunday with a suspected calf injury.

While the Tongan international initially kept warm for the rest of the first half on a stationary bike, Manly communicated after the half-time break that the back-rower would not return.

It remains unclear how serious the forward's injury is, with Maguire due to name his squad for game two next Sunday.

With Olakau'atu off, the Sea Eagles lost one of their most damaging ball runners and were unable to hold on to a hard-fought lead.

The defeat leaves coach Anthony Seibold with just one win in his past five games as the Sea Eagles slip to 10th on the NRL ladder.

Brian To'o was a big reason the Panthers were able to turn the tide, the workaholic winger bagging a first-half hat-trick and churning out 213m and 14 tackle busts.

To'o showed few signs of rust backing up from Origin when he scored the first try of the afternoon in the 12th minute, before Manly counterpart Tommy Talau ran riot.

Talau posted a hat-trick in the space of eight minutes, sent in by Tolu Koula and Ben Trbojevic for his first two, before a bending Luke Brooks banana kick went over the top of Sunia Turuva and into his arms.

The radar on Reuben Garrick's right boot was off and a six-minute double salvo from To'o, both of which were converted by Paul Alamoti, gave the Panthers a 16-12 lead at halftime.

Alamoti kicked a penalty goal early into the second half after Nathan Brown was penalised for a hair-pull on Jarome Luai to open up a six-point buffer over the Sea Eagles.

It was a lead the Panthers wouldn't relinquish, Turuva adding a double and prop Liam Henry crossing to further hammer home Penrith's advantage in the second half.

Talau and Jasob Saab offered some response for Manly, but they left their charge too late as the Panthers won to hold on to third spot on the NRL ladder.