The home side went ahead through Ola Toivonen in the 23rd minute on Sunday but saw their progress stunted by an equaliser from Robert Braber on the stroke of half-time.
RKC held their own in the second half until Sander Duits was dismissed with five minutes to go and the 10 men could not hold out as Locadia struck to deny the struggling visitors just a sixth point of the season.
PSV now have 18 points from nine games, the same number as Twente, who won 1-0 at Cambuur on Friday night.
Ajax are a point behind the top two after beating FC Utrecht 3-0 at the Amsterdam ArenaA thanks to goals from Thulani Serero, Davy Klaassen and Danny Hoesen.
Feyenoord moved up to fourth courtesy of a 2-1 win at Vitesse Arnhem.
Goals from Stefan de Vrij and Graziano Pelle inside the opening 20 minutes proved enough for the Rotterdammers with Mike Havenaar's 83rd-minute consolation proving too little, too late for Vitesse.
Managerless AZ Alkmaar slumped to a 2-1 loss at FC Groningen.
The visitors, under the guidance of interim boss Martin Haar following last weekend's surprise sacking of Gertjan Verbeek, slipped to defeat thanks to Groningen substitute Richairo Zivkovic.
Zivkovic struck with 19 minutes to go after AZ's Johann Berg Gudmundsson had cancelled out an own goal from Nick Viergever.