Police Tero punished BG Pathum United for another error-strewn display by the defending Thai League 1 champions, winning the away battle 3-0 on Saturday night.
It was a second straight loss for the Rabbits, who won the top flight for first time last season after picking up only one defeat in 30 games.
The result has thrown Pathum United's bid to retain the trophy off the track as they are now spotted in 11th place with just seven points from five matches.
Police, who had a mediocre run in the league last season, find themselves tied for the fifth place with eight points from seven games.
Police continued their giant-killing spree with a fine show last night as they backed up their Tuesday night's 2-0 victory over Chonburi with another winning effort.
Wanchai Jarunongkran (14th minute) and Jenpob Phokee (50th) had put Police on course to a deserving victory before Nattapol Sukchai rubbed salt into the Rabbits' wounds on 88 minutes.
Former champions Chiang Rai United claimed valuable three points with a 2-1 victory at promoted Nongbua Pitchaya last night.
Chotipat Poomkaew netted the winner for the Beetles near the hour mark after Nongbua's Hamilton Soares had cancelled out an early strike by Felipe da Silva.
Visiting True Bangkok United beat Nakhon Ratchasima 2-0 in another match last night. Vander Luiz netted the first goal in the 40th minute and Heberty Fernandes added another to the tally in injury time.
