It may still be improbable, but the Western Force still retain the slimmest of Super 14 semi-final hopes after downing the Cheetahs 45-17 at Subiaco Oval.

Needing to first achieve a win and four tries, before hoping for other results later, John Mitchell's side held up their end of the bargain with a record score.

Force backs Ryan Cross, Digby Ioane and Scott Staniforth were all beneficiaries of ambitious first-half handling and playing, while the oversized tourists looked out on their feet at 21-0 down at the break.

But in a creditable reversal, the South Africans returned from half-time invigorated, Phillip Burger and Ryno Van Der Merwe hitting back with tries, until the unlikeliest of candidates, prop AJ Whalley, secured the Force's bonus point.

Tai McIsaac, Staniforth and Cross all crossed late to extend the Cheetahs record of never having won in Australasia - and ensured Ollie Le Roux's last Super rugby appearance on foreign soil ended disappointingly.

Mitchell said his men had no choice but to attack.

"It is great to keep ourselves alive ... it had to be done, and it is going to be a big contest next week," Mitchell said.

The Waratahs were unable to do the Force a favour by beating the Chiefs earlier, leaving the Perth side's semi-final hopes reduced before kick-off.

But the Sydney result had not changed the Force's requirements for a raft of five-pointers, and they soon showed their intent.

Early overlaps and kickable penalties were both spurned until Matt Giteau knocked spots off the Cheetahs's defence.

A step and pass out of the back of the hand freed Cross and, just four minutes later, the tourists were carved up again, with Ioane showing why Queensland are so keen for him to go home next year.

Any friction from the winger's decision to go back on the agreement with the Force did not appear on the field, but referee Paul Honiss was getting tetchy with the Cheetahs' desperate attempts to slow the play.

The Kiwi, officiating in his 200th first-class match, finally lost patience in the last moments of the first half, yellow-carding Duayne Vermuelen for repeated infringements.

And his absence was immediately capitalised on when James Hilgendorf fed Staniforth for his first try of the season, following his nine five-pointers last year.

After Force fullback Matt Henjak failed to appear for the second half, his side's slick movement was disrupted and, allied to a distinct improvement from the Cheetahs, a stroll turned into a struggle.

Burger crossed for the Cheetahs' first points after rapid ball movement, and then the slowest of motion in a rolling maul allowed Van Der Merwe to flop over to make it interesting.

But after McIsaac showed off the handling he learned in his junior water polo days, Whalley popped up on the wing to sprint over for the all-important fourth.

McIsaac's slick hands then started and ended the move of the night, before Cross and Staniforth both completed doubles.

And although they still need to win the equivalent of the results lottery while beating the Blues with a bonus point themselves next week, the Force still cling to hopes of a fairytale finish.

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