Brisbane Roar coach Ange Postecoglou issued an ominous warning to A-League rivals, saying his team still have the potential to improve.The Roar's status as the league benchmark was enhanced with a 1-0 away victory over second-placed Adelaide United on Sunday night, despite missing prime movers including captain Matt McKay (Socceroos duties), influential midfielder Thomas Broich (groin) and defender Ivan Franjic (hamstring).The triumph took Brisbane's undefeated streak to 19 matches, a feat Postecoglou said was "extraordinary"."Crazy as it seems, we don't really talk about it," he said of the record sequence."Our whole emphasis this year has been about playing good football and that is all we worry about each week: can we go out there and play as well as we possibly can in our style and get better every week."The Brisbane boss said there was no reason for his side, now 11 points clear at the top of the table, to dip in form ahead of finals."Our challenge to these guys is to every day get better, why should you stop?," he said."There's no reason why there should be a drop-off, I don't see any reason."And certainly the player's attitude, the feeling amongst the group, and what we challenge them with, is let's just keep going and don't set a target."If our target was to finish top spot we might have taken our foot off the pedal a little while back but that wasn't our target."We didn't have targets."We just every week want to play as best as we can and see where that takes us."From our point of view we're not sitting there going two more games and we've won this thing."What we're saying is there's six more games in the league and we want to play our best football in these six games and play our better football in the finals."The Roar have lost just once this season, in September against Melbourne Victory, in a competition Postecoglou said wasn't "designed for long unbeaten runs"."A team will do three or four, five games," he said."With the salary cap, so many games in such a short space of time, it is inevitable you will have an off day, but we haven't."I think during this 19-game run there hasn't been a game where I have walked away and thought we didn't deserve to get a result."I think in every game we have performed to a fairly consistent level."