KKR are ahead of RR on net run-rate but Kallis said: "Winning will be the priority."
Rajasthan Royals kept alive their play-off hopes by beating defending champions Mumbai Indians by seven wickets with two overs to spare on Sunday night.
Samson has so far scored 178 from 3 matches at 89 with strike rate of 163.30.
Both the teams have 4 points but RR have played a game less than KKR.
RR perished with a thrilling nine-run win over the defending champions.
Watson fired Rajasthan to an imposing total of 199 for 6 with a dominating 59-ball innings of 104 not out.
Rajasthan Royals defeated Kolkata Knight Riders by nine runs in a virtual knock-out.
Kolkata's chances of making it to the play-offs look very tough as they have secured 15 points from 14 games.
RR secured their passage through to the IPL 2015 playoffs.