Penrith's 16-0 loss to Melbourne on Thursday was the Panthers' second defeat in their past three matches and has raised hopes among their rivals that the premiers - who looked invincible a month ago - are vulnerable.

With Nathan Cleary suspended and Jarome Luai injured, the Panthers have been brought back to the pack heading into the final three weeks of the regular season.

While the Panthers will almost certainly claim the minor premiership, due to their six-point lead at the top of the NRL ladder, the loss to the Storm was the first time Penrith have failed to score in seven years.

With Liam Martin suffering an ankle injury in the defeat and Shaun Edwards (sternum) a late out, concerns are mounting for Ivan Cleary.

Cleary will have his son and star halfback back for finals while Luai is expected to return after the first week of the play-offs but the Panthers' will be limping rather than purring into September.

In contrast several of their rivals are finding some great form at the right time of the season.

Ryan Papenhuyzen's year-ending knee injury last month appeared to have left the Storm's season in tatters as they slumped to a four-match losing run.

Four weeks later, with Cameron Munster calling the shots at fullback, the Storm are now back among the competition's genuine contenders.

The Sydney Roosters are another powerhouse making a late surge.

A second year without finals under Trent Robinson was looming large after losses to Melbourne, Parramatta and Penrith before the bye.

Fast forward six weeks and the Roosters have won five straight to be a genuine premiership threat heading into finals.

Last year's beaten grand finalists, South Sydney, are also looking ominous.

The Rabbitohs demolished Parramatta 26-0 on Friday night and have superstar Latrell Mitchell hitting his best after missing most of the early part of the campaign.

While the Storm, Rabbitohs and Roosters are running hot, Cronulla and North Queensland are also in the hunt having been leading lights all season.

The Cowboys fell to the Roosters at the SCG on Saturday in a emotional game following the tragic death of premiership-winning coach Paul Green earlier in the week.

But Todd Payten's team are still leading the way in the race to finish second on the ladder behind Penrith - a spot that would give them a double chance and home advantage in the finals.

The Sharks, under first-year coach Craig Fitzgibbon, have also picked up 15 wins after demolishing Wests Tigers 36-12 in Tamworth.

With eight wins from their past nine games, the Sharks have consistently overcome injury woes in recent weeks and have a nice run home with games against teams outside the top-eight remaining in Manly, Canterbury and Newcastle.

With the mercurial talents of the Eels and Brisbane set to be the other teams in the top eight, it all adds up to an unexpectedly unpredictable finals campaign.

Australian Associated Press