Both teams had picked up bonus-point victories from their opening two fixtures, so something had to give at Newlands this weekend.
And, while it was the Lions who dominated possession for the most part, the home side took their chances well and defended resolutely to pick up the four points.
Lions coach Johan Ackermann was forced to reshuffle his XV for the trip to Western Province after fly-half Jaco van der Walt sustained a knee injury during last weekend's win over Eastern Province Kings.
And Western Province set out to expose any weakness in their opponents' line-up, putting the first points on the board 12 minutes in.
Kobus van Wyk touched down after some good work by Cheslin Kolbe before desperate defence turned into a lethal counter-attack as the centre went over for the second time five minutes later.
At 14-0 up inside 17 minutes, Western Province were threatening to run away with the match, but had to withstand significant pressure from their opponents for much of the remainder of the match.
Van der Walt's absence was felt in attack as stand-in fly-half Stokkies Hanekom struggled to have as much of an influence on the game, making the home side's defensive task easier.
But, after Ruan Combrinck had pulled back three points from the tee, Stephan Coetzee went over in the corner to reduce the deficit to six at the break.
Demetri Catrakilis and Combrinck exchanged penalties after the interval - the former converting two to the latter's one - before replacement Jaco Taute recovered from an intercepted pass to scoop the ball up and put the result beyond doubt eight minutes from time, Kurt Coleman adding the conversion.
In the day's early kick-off, Blue Bulls picked up their first points of the campaign with a 30-25 win over Eastern Province Kings at Loftus Versfeld.
Akona Ndungane ran in two second-half tries as the Bulls kept their noses in front having led 11-8 at the interval, while the Kings picked up a losing bonus point.
Saturday's remaining fixture saw Natal Sharks dramatically battle back from a 13-3 deficit at the break to earn a 19-16 victory over the Free State Cheetahs.
The sides were tied at 16-16 heading into the final three minutes before Fred Zeilinga converted a 40-metre penalty to put the Sharks in front for the first time in the match.
The four points see the Sharks remain within a point of the Lions at the summit.
In Friday's only match, Pumas beat Griquas 33-15.