Scotland fly-half Finn Russell knows that Vern Cotter's men cannot afford another sluggish start when they face Australia in their World Cup quarterfinal at Twickenham next week.

Russell overcame an ankle knock to return for the 36-33 win over Samoa at St James' Park that earned the Scots a berth in the last eight, having fought back from 26-23 down at half-time.

It was the fourth successive match in which a slow start threatened to undermine an otherwise resolute Scotland performance, something Russell concedes his side still need to address as they begin their build-up to the showdown against the Wallabies next week.

Russell said: "It's disappointing not to have the first half we wanted again, but we have to give credit to Samoa who were outstanding, and we knew what we had to go out and do in the second half.

Greig Laidlaw of Scotland scores a try © Getty Images

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"We can take some positives out of the game - we were outstanding at the set-pieces - but we also know there are some things we need to improve. We know what we have to do and from now it is knockout rugby and that's all that matters."

Centre Sean Lamont collected his 100th cap for Scotland, and fired a warning to their World Cup rivals to underestimate them at their peril.

Despite the nerve-shredding finale to his side's Group B campaign, Lamont believes Scotland have never been better equipped to seize the initiative and march even further into the tournament.

"This is by far the best Scotland team I've been involved in in my 11 years of playing -- not just in the talent but the way the boys fight for each other," Lamont said.

"We've got a lot of belief and the general team spirit is brilliant. We can go a long way if we continue to show that level of belief and confidence.

"We are ready for next week and of course we will be the underdogs, but Scotland relish being the underdogs. You can take us for granted all you want, and you'll get a bite on the arse."

Scotland's struggle to assert themselves in the early stages of their Group B pool matches threatened to cost them dear as they trailed the already-eliminated Samoans 26-23 after a high-octane first half.

But the canny boot of Greig Laidlaw once again saved the day with the scrum-half scoring 26 of Scotland's points, including, fittingly, the last of three tries which finally put the game beyond their plucky opponents.

Meanwhile Lamont, who coincidentally won his first Scotland cap against Samoa in 2004, said his personal achievement paled into insignificance compared to his country's march into the last eight.

Lamont added: "It's a great feeling to win 100 caps but I didn't really care if I got on the field -- it was all about Scotland winning and that was my main focus today.

"I'm really happy to have got it and it's a big milestone for me, but during my time in the team I have realised it is about the team first and the individual second, and that's the kind of squad we are."