Cape Town - Proteas skipper Faf du Plessis revealed that a few tired bodies in the South African camp is a concern following their thrashing by Pakistan at the Wanderers on Sunday.
A terrible batting collapse saw the Proteas bundled out for 164 in 41 overs at the Bullring.
Pakistan cruised to their target with 111 balls to spare as the tourists won by 8-wickets and broke the Proteas' unbeaten PinkDay winning streak.
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The series is no all square at 2-2 with the decider set for Cape Town on Wednesday.
Du Plessis assessed the Proteas performance as 'average' and believes he is gaining further insights for the Cricket World Cup in May.
"There was some average cricket from us, but some very good cricket from Pakistan. It's tough to look at the positives," Du Plessis told reporters in Johannesburg.
"I'm picking up lots of valuable lessons about the balance of the side, looking at what we're missing at the moment. Even though we are losing, I assume the younger guys are getting a lot of experience. I can speak for myself, even when losing, there's clarity on how I see us moving forward with the team."
Following Pakistan's tour, Sri Lanka visits South Africa for two Tests, 5 ODIs and three T20s with the Indian Premier League starting in March before the Cricket World Cup in England.
"That's in the back of my mind when I can see that some of the guys are tired, mentally and physically," said Du Plessis.
"It's a balancing act, we've got a big game that's coming up but it's really important that we also make sure that we have guys getting enough game time as well.
"I think we're going to try and rest the Test squad players for the T20s. Right now, I can see that there's a few tired bodies on the field and that's a concern."
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The deciding fifth and final ODI starts on Wednesday at Newlands (13:00).