Pieters only turned professional in June last year and secured his European Tour card via the Qualifying School at this venue in November, aided by an opening round of 64.
The 22 year old said: "It was a solid day. I hit solid shots and really played to my strengths. I got two over par early just because my short game wasn't sharp enough but I took advantage of the par fives again today and the shots dropped in the end.
"I stayed really patient, you need to be on this course and I'm getting better and better at it. You know that it's going to be a hard day and an even par is a good score.
"I've always done well on really tough courses, I like grinding it out, not having to shoot six or seven under. Today I shot one under and I'm in the lead.
"I'm excited for tomorrow. I'll just go out to play golf, obviously playing for a win too.
"Playing with Jiménez will be fun, I'll get to learn a lot from him and I'll just soak it all in. I've never played with him or any of the big names. The crowd will also be bigger and all the support will go to him but I just have to play my own game."
Jiménez surged two clear of the field thanks to six birdies in his opening 13 holes at PGA Catalunya Resort, but bogeyed the 15th and 18th to card a third round of 69.
That left the 50 year old, who was fourth in the Masters Tournament last month and then won on his Champions Tour debut seven days later, on five under par and allowed overnight leader Pieters to reclaim top spot with birdies at the 15th and 16th in a round of 71.
"I'm a little disappointed with that," admitted Jiménez, who has no plans to switch to the seniors circuit as he chases a fifth Ryder Cup appearance at Gleneagles in September. "I didn't hit it very well the last few holes."I played very well the first nine holes and was solid until the 14th but made a bad bogey on the 15th where I three-putted from eight metres and also bogeyed the last."
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