Samoa took a big step towards the rugby league World Cup semi-finals with a dogged 20-12 win over arch rival Tonga in their island derby at Penrith.

Samoa will clinch their pool if they beat Ireland in the last pool match at Parramatta next Wednesday.

The clash featured plenty of rugged defence and jarring hits, plus occasional high tackle.

And when it was over, hundreds of excited Samoa fans charged onto the pitch to celebrate.

While it wasn't the spiteful battle some pundits had forecast, Australian referee Shayne Hayne still had his work cut out.

He placed two players on report - Samoan prop Kylie Leulua'i for a high tackle on Tongan fullback Fetuli Talanoa in the first half.

After the break, Hayne placed Tongan centre Etu Uaisele on report for a dangerous tackle on Samoan fullback Smith Samau, who was picked up and driven into the ground.

Samoa grabbed initiative early, with winger Francis Meli crossing in the third minute.

And they bolted to a 10-0 advantage in the 11th minute, when skipper Nigel Vagana picked off pass from Tongan hooker Tevita Leo-Latu and sprinted 90m for a try converted by Ben Roberts.

Tonga surged back into the game when classy centre Michael Jennings charged onto a brilliant flick pass from Tony Williams. The conversion cut the deficit to four points.

Vagana missed a glorious opportunity for another try when he dropped the ball over the line in what effectively became a 12 point turnaround.

Just a couple of minutes later Leo-Latu burst out of dummy half to set up a 12-10 Tongan lead.

Bulldogs NRL star Matt Utai weaved over in the right hand corner to give Samoa a 14-10 halftime lead.

But it was virtually one way traffic in the second half, with Samoa dominating possession against an outfit clearly still fatigued from last Monday's win over Ireland.

Samoa extended their lead with a brilliant try to centre George Carmont, who capitalised on some sensational lead-up work by forwards David Solomona and Lagi Setu.

The dominant Samoans had potential tries to Carmont and Ben Roberts rubbed out, but continued to monopolise possession until the closing minutes.

Tonga was further hampered by an apparent groin injury to halfback Willie Manu.

The result effectively eliminated Tonga, with Ireland needing to beat Samoa by six points to top the pool.

Vagana placed Friday night's game alongside his Test debut for New Zealand as one of the highlights of his career.

He admitted it hadn't been easy to control all the hype around the first World Cup fixture between the ancient rivals.

"The rivalry is instilled into you when you are born and it's something that we always have and it's always within us and trying to stay focused and not let the emotion take over can be a stretch," Vagana said.

"It's to the credit of us and the Tongans that we played a very disciplined game, no fights, no brawls or anything like that."

Samoa coach John Ackland praised Tonga for their courageous defensive effort in the second half.

"We always thought that they would tire but, to their credit, they didn't, they kept defending their line with tremendous courage," Ackland said.

Tonga coach Jim Dymock refused to use the short five-day turnaround as an excuse for their second half performance and said Samoa played well.

"We played well in patches, I just thought we played dumb some times, maybe we go caught in the hype a little bit in the second half," Dymock said.

Both coaches felt the game was a great advertisement for the international game and especially the Pacific Islands style of football.

Tonga captain Lopini Paea paid credit to the physicality of the Samoans, lightheartedly referring to the "13 big gorillas".

Paea said he didn't object to getting mobbed by the crowd at the end.

"It would have been better if you get mobbed when you win, I'm surprised I didn't get jumped by a couple of Tongan fans," joked Paea.

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