Ospreys face a “cut throat” European Champions Cup tie on Sunday against an Exeter side who have not lost at home this season, says James King.
Winning would guarantee the Welsh region reach the knock-outs for the first time since 2010.
Number eight King says Exeter’s home record is “brilliant”, adding: “We know what we need to do.”
Clermont Auvergne host Bordeaux-Begles at the same time with all four teams in the group capable of progressing.
“Our fate is in our own hands. It’s coming down to the last game,” said Wales Six Nations back-row challenger King.
Ospreys battled to pole position having often struggled in the Pro12 this season, beating Exeter in the opening round and picking up valuable losing bonus points in Montferrand and Bordeaux.
And after Clermont went into a 13-6 lead at Liberty Stadium last weekend, Ospreys fought back to win 21-13.
Ex-Wales and Ospreys back-five forward Jonathan underlined what it would mean for them to reach the last eight this time around.
“It’s what everyone craves, isn’t it, players and fans alike- and six years ago is a long time.
“I think the ironic thing this season for the Ospreys is that everyone was writing them off because things haven’t been going too well in the Pro12 in recent months.
“But obviously they’ve turned that around, they’ve had some good form – particularly over Christmas – and the win on the weekend was outstanding.”
How they stand
Rarely, every team in this pool goes into the final round with qualification for the knock-outs still possible.
If the Ospreys win, they are through. Any other result and the complications begin.
Draws, bonus points for losing by seven points or fewer; scoring four tries and getting four touchdowns in a defeat or a draw – those are the connotations the Welsh team hope to avoid.
A point would take Ospreys out of reach of Exeter and Bordeaux-Begles, who are tied on 11 points each.
That would leave Wales centre Jonathan Davies and his Clermont team-mates are the biggest threat to Ospreys’ position at the top of the group.
Clermont are favourites to see off their French rivals Bordeaux on Sunday and a straight win for them at the same time Ospreys lose might end the Welsh team’s campaign.
At least the Pool Two games are the last of the weekend – every team in it will know what has to happen if they are to progress.
The Exeter view
Exeter boss Rob Baxter hopes his side, who lie second in the English Premiership, can overcome the odds with the help of a Bordeaux win in Clermont and top the group.
But he accepts: “Realistically you would say no, but that’s not at the forefront of my mind.
“At the forefront of my mind is the performance we put in this weekend.”
Baxter is particularly keen his side ensure Exeter show they are “a better team than probably we produced when we went up to Ospreys”.
He told the media: “You say people expected us to win – the truth was Ospreys had a team full of internationals and probably a bit more experience in the Champions Cup than us.
“And fair play to them. They dealt with the whole day way better than we did – we’ve got to take that on the chin and keep developing the side so that when those days come around, we deal with it better than the opposition.”