Star went down 63-56 away to Tralee in the All Ieland Superleague on Saturday night as the home side swooped in the final quarter to take the win.
Leading 35-31 at half-time in front of a sell-out crowd, Star also led 49-47 going into the final quarter. Coach O'Neill said: "We just couldn't put the ball in the basket, that's what hurt us.
“Defensively we did very well, the guys have got the intensity and aggression that we need, but we have to start putting things right at the other end of the court.
"This week I'll be demanding a lot from the guys in training when it comes to shooting because it's just not acceptable at the moment.There was a real buzz after the win in our opening match and now I want to see how they react to this defeat."
Belfast Star Top Scorers: Greg Womack 15, Patrick Mullan 10, Conor McElroy 6. Tops for Tralee were: Dusan Bogdanovic 22, Ryan Leonard 16, Darragh O'Hanlon 6.
In other games:
UCD Marian produced champagne basketball to stun UCC Demons 103-82 in the battle of the colours at Belfield.
DCU Saints got back to winning ways when defeating Moycullen 76-74 at NUIG. Saints paved the way for the win with a solid first-half performance that saw them take a 14 point interval lead.
Griffith Swords Thunder have displayed serious form in recent weeks and their 84-57 win over Eanna sets them up nicely for their clash with Demons in Cork on Sunday.
The derby game between Templeogue and Killester in Dublin yesterday was a terrific encounter with the former taking the honours 82-74.