Cronulla's premiership defence is now in full swing, after claiming their fourth straight NRL win with a comprehensive 28-2 wipe-out of Penrith on Sunday.

One week after holding out Melbourne in a Grand Final rematch, the Sharks again kept their try-line intact to stun the 15,780 at Pepper Stadium and retain their top-four spot.

Not since 1994 have the black, white and blue been perfect in defence in back-to-back weeks, including their record 15-game winning streak last year.

The visitors led 16-2 at halftime, when Sharks centre Jack Bird crashed over just after the resumption and then skipper Paul Gallen did likewise in the 60th minute to seal the win.

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The Panthers had plenty of opportunities to exert some scoreboard pressure early in the first half, but were constantly repelled by the Sharks' trademark defensive grit.

By the main break, the home side had forced more errors out of their opposition and enjoyed twice as many plays inside the opposition 20-metre line.

But last year's entertainers had nothing to show for it and were left frustrated by the rushing defensive line of the Sharks, who, by contrast, had no such trouble crossing the stripe.

Halfback Chad Townsend grubbered through for halves partner James Maloney in the 17th minute, before Sosaia Feki finished off a simple left-side shift for a decisive try in the 37th.

Not even the return of several troops, headed by skipper Matt Moylan, and backline flyers Tyrone Peachey and Waqa Blake, could inspire the Panthers out of their rut.

Any chance of a Panthers fightback after halftime quickly dissipated, with Bird and Gallen's double-blow, meaning serious questions must now be asked of the pre-season favourites.

On an afternoon when there were even contributions across the board, Sharks fullback Valentine Holmes was arguably his side's best, with a team-high 166 metres and three tackle busts.