"The Chiefs have been the best team in the competition this season," Pietersen said. "They have showed that with their consistency across the whole tournament, and we're in for a huge encounter.
"They have a great attacking game, they have some fantastic attacking backline players as well as big-game loose forwards. Then you have a guy like [front rower] Sona Taumalolo, who has scored nine tries off pick-and-goes close to the line, so they are dangerous all-round," he said.
"They also have a good defensive system and will definitely challenge us when we have ball in hand."
Pietersen said the Sharks would struggle if they did not start well.
"We must keep them at bay in the first 20 minutes. If we want to win this game, we need to be at our best and everyone needs to bring his 'A' game.
"It's going to be very tough, it's going to be physical, and if we don't front up and take them on at their own game, we will have a long day. But it's all about the good start and building from there," the winger said.
Pietersen said the Sharks would look to emulate what they achieved against the Stormers last week.
"We went into that game with a plan and stuck to our structure, and knew that with knock-out rugby, it was the team that took its opportunities that would come out on top. We knew we would have to start well against them to be in the game, and we did. We knew we could not afford to be behind going into the final quarter, and we were not."
Pietersen scored a wonderful try in that match and he has been having a great season.
"I'm happy that my body is in great shape, for just about the first time in my career," he said. "I'm fully fit and feeling very strong, which adds confidence. You play well and your confidence rises and motivates you further."
Pietersen said his good form was also related to the growth the team had showed since losing to the Lions before the break for the test series against England in June.
"The development of our team came together when the inexperienced guys started to gel with the experienced, and everyone began playing their best rugby," he said.