Bok's charges were looking to bounce back from last weekend's 3-2 loss to Albirex Niigata on Sunday when they entertained DPMM, but they fell behind in the 17th minute through a Basiru Osman strike.
Japanese winger Tatsuro Inui then equalised for the Warriors with a stunning freekick in the 68th minute, and while the home side had plenty of the ball in the second half, they failed to carve open any real chances.
And SAFFC ultimately lost the game when DPMM striker Shah Razen capitalised on some indecisive defending to grab the winner for the visitors, something Bok is looking to eradicate.
"I thought we had more of the game, but again we allowed the opposition to score [from] some set-plays," Bok said on the club's official website.
"Our concentration let us down once more and we have to work a lot more on that before our next game against Home United."
SAFFC captain Daniel Bennett echoed his coach's sentiments, although he felt his side had performed well overall.
"There was a mix-up for one of the goals, but I think as a unit we played well enough."
Bok did give credit to his side for the amount of work they put in, and remained hopeful their performances would improve once Japanese trio Inui, Shimpei Sakurada and Seiji Saito, who all joined in pre-season, get acclimatised to life at the Choa Chu Kang Stadium.
"I think the boys worked very hard, but the three new Japanese players are taking some time to adjust to their new team-mates, which is understandable," Bok added.
"We just have to work even harder from now on to get things right.
"We knew we had a tough opening three games and unfortunately we've lost the first two. We'll be looking to put that right in our next match against Home United."
The Warriors are currently 12th in the S.League, while Home will also be looking for their first win of the season next Sunday, after draws against Balestier Khalsa and Gombak United.