Bolton lost 3-2 at home but put up a spirited display, undone by conceding three first half goals.
Cullen signed for Bolton just days ahead of the game alongside with West Ham defender Reece Burke, who came on as a second half substitute.
The Republic of Ireland youth international spent last season on loan at Bradford City and this is his first taste of Championship football.
While he struggled to make an impact early on, Cullen grew into the game and was a danger from set pieces.
The 21-year-old played all 90 minutes of the defeat, and worked hard to try and get his team into attacking positions.
The home defeat was disappointing but Cullen showed he has the potential to be an asset this season if manager Phil Parkinson keeps faith in him.
Cullen needs to be a success at Bolton if he is to crack the West Ham first team and yesterday was tentatively positive first step.
Here is a look at how fans reacted on Twitter to his performance...
Players have to learn from today. Promotion honeymoon is over! Concentration first half was poor. Cullen very impressive, Madine MOM! #bwfc— John Hall (@OneSizeFitz89) August 6, 2017
Some positives to take out the game. Burke, Cullen, Buckley and Armstrong all need to involved. #BWFC. Can see the difference in movement— Adam Mason (@adammason1991) August 6, 2017
Plenty to work on especially at the back. Get the ball on the deck more Cullen will do well for us. Showed some fight 2nd half #bwfc— Stephen (@SA_JNR9) August 6, 2017
Considering Cullen and Burke only joined up with the team this week, I'm very positive about them. Buckley, Armstrong also looked good #bwfc— Danny (@TrottersDan) August 6, 2017
Thought Cullen looked very tidy on the ball on the occasions that he had it. We definitely need to use him more #bwfc— Russell Carr (@RussCarr3) August 6, 2017
Second half much better. Defensively alot of work needs doing, Cullen looked a great asset. Took some injury blows onto Crewe weds #BWFC— Ryan Spackman (@squintyeyes90) August 6, 2017
Josh Cullen must wonder why he's joined! He must have neck ache by now #bwfc— Mr Ecky (@bwfc_85) August 6, 2017