Sydney Roosters coach Trent Robinson says he is unconcerned by his side's repetitive second-half struggles, after their last-minute 18-12 loss to Manly.

The Roosters are still yet to win a second half this season, despite going through their first four games unbeaten, before Friday's upset loss.

Their aggregate score is now a 56-40 record against in the second term, however they did walk out equal against Penrith and South Sydney in the final 40.

By comparison, their first-half record reads 74-22 in their favour.

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But Robinson said Friday night's second stanza was far different to the four second-half efforts that had preceded it.

"The second half was disappointing, the way we finished that," Robinson said. "But very different to the other four."

In three of their opening four clashes, the Roosters had the match well in their control at halftime, while in the other, against Penrith, they were able to hold on for the win.

On Friday, they struggled to gain momentum in a wet second term that saw them make six handling errors.

After going to the break at 6-6, Sea Eagles centre Dylan Walker scored two tries in the final 13 minutes to claim the match.

"It was stop-start in the second half," Robinson said. "But the first half was pretty free-flowing and it was hard for us to see who was going to come out in top of that one."

The loss was the Roosters' first of the season and could also come with the added cost of losing Queensland Origin contender Dylan Napa for the next month, after a suspected ankle syndesmosis injury.

It comes at a crucial time for the Tri-colours, who face a fearsome forwards battle with Brisbane next Thursday at Suncorp Stadium.

Robinson refused to buy into the thought that the loss may have been a wake-up call for the side.

"There's never an opportune time to lose," he said. "It's disappointing to lose our first game, especially in a game that was there to be taken."