The Panthers on Sunday threatened to repeat last year's famous round-one comeback when they whittled a 14-point deficit to be within two.

But the Eels, already showing sterner stuff this year, held on despite losing Michael Jennings to the sin-bin at a critical juncture in the second half.

Eels coach Brad Arthur said their defensive resolve, which included two Mitchell Moses try-savers, reminded him of the side who went to the finals in 2017.

"We didn't look like that last year. Regardless of the result today, I was proud and happy that we looked like that team again," he said.

The win might have come at a cost, with key prop Nathan Brown suffering a suspected torn pectoral that could rule him out for up to three months.

A resolute Eels defence had kept the home side scoreless for almost an hour at Panthers Stadium, but the game turned on Jennings' sin-binning.

The Eels' centre denied Maika Sivo a maiden NRL try after knocking Isaah Yeo out with a swinging arm that ended him with him being placed on report.

Wayde Egan scored not long after, and the 12,604 crowd roared to life when James Tamou barged over soon after.

However, Jennings sealed the two points when he took a perfectly timed pass from debutant Dylan Brown in the closing moments.

The 18-year-old Brown was among the Eels' best, showing plenty of classy touches to take some pressure off his senior playmaker Moses.

There was plenty of anticipation entering the second Cleary era at Penrith, however the home side couldn't have made a worse start.

Numerous mistakes and penalties deep in their own half resulted in the Eels enjoying a 22-4 first-half advantage in plays inside the opposition 20-metre zone.

The visitors were also more adventurous with the ball, offloading seven times to one that translated into a two-try lead at the break.

Penrith forward Hame Sele might have broken his forearm in his club debut.

Cleary said his team's ill discipline - they were caned 10-2 in the penalty county - cost them any chance of stealing victory.

"There was a couple of poor penalties we gave away in the second half. We had to play with more control because the clock was on our side," he said.

"The game was turning our way.

"I thought we had every right to get that game in the finish. But we only completed one set in the last 15 minutes when it was 14-12. That was disappointing."

Australian Associated Press