Kagiso Rapulana (76), Niel Bredenkamp (74*) and Kyllin Vardhan (52) all scored half centuries to ensure their side a commanding position.
Dane Paterson dismissed key batters to deny Niel Bredenkamp who finished undefeated on 74 runs (11 fours, 1 six) an opportunity to score a century. He finished with 3/76 in 19 overs and was assisted by the economical George Linde who returned with figures of 2/47 in 21 overs.
Sharn Gomes and Matthew Kleinveldt gave WP a positive start of their second innings when they shared a 62-run opening partnership. The breakthrough finally came just two overs before close of play when Gomes was trapped lbw for 35 runs by Friedel de Wet.
At close of play WP are 66 for 1 in 20 overs in the second innings. They trail by 36 runs with nine wickets remaining.