Rugby World Cup 2015: How Scotland can reach the last eight

Head coach Vern Cotter looks on during Scotland's training session

The mighty frames of Samoa's XV stand between Scotland and a quarter-final place at the Rugby World Cup.

South Africa's rout of the United States on Wednesday means they have won Pool B.

Scotland are second and, as they prepare for Saturday's match in Newcastle, they know that staying there ahead of Japan will guarantee a last-eight tie against Australia or Wales from Pool A.

If Scotland beat Samoa...

To qualify on Saturday at St James' Park, Scotland must beat fourth-placed Samoa. That would put Vern Cotter's side out of Japan's reach.

Should Scotland lose...

However, if they were to lose to the Pacific Islanders, Scotland might yet find a reprieve in Gloucester the following day.

That is when Japan play the USA who, like Samoa, cannot progress in the tournament.

If Scotland lose on Saturday by more than seven points, thereby failing to claim a losing bonus point, and Japan win on Sunday, Japan go through.

But if Scotland lose to Samoa and Japan lose, Japan will be out.

If Japan draw and win two points, again their World Cup will be over because, although both teams would have 10 points, Scotland would be ranked higher since they won the head-to-head match.

Samoa head coach Stephen Betham and his players will want to end their World Cup campaign with a win

There are a few caveats, though. If Japan draw but gain a bonus point for scoring four or more tries, they would go second with 11 points.

However, if Scotland were to gain two bonus points in defeat to Samoa (for scoring four or more tries and for losing by seven points or fewer) and move to 12 points, Japan would need a bonus-point win to secure qualification.

And a draw?

Finally, should Scotland draw with Samoa without scoring four or more tries, they would be four points ahead of the Brave Blossoms when they kick off at Kingsholm.

Japan would need to beat the USA with a bonus point to take second spot.

Cotter will surely tell his players to forget about any such complications. His message will be simple - go out and beat Samoa!