Wins over Vasteras and Degerfors had reignited Sirius' hopes of a maiden title after a dismal spell in the middle of the season, and by beating relegation-threatened Orgryte, they have gone 10 points clear of Djurgarden and Hammarby, both of whom will be in action on 20th September.
The away side were in front inside seven minutes, as Isak Bjerkebo curled in a cross from the left and Henrik Castegren headed it home. OIS had chances to equalise before the break, but Sirius gave themselves breathing space just after the hour mark when a long period of attack ended with Zalan Vancsa tucking the ball inside for Victor Svensson to finish.
The hosts pulled a goal back in added time when Sebastian Lagerlund rose at the back post to nod in Tobias Sana's corner, but it was too little too late for Orgryte, who remain four points from safety having gone seven league games without a win.
Having thrashed AIK away from home last time out, Vasteras saw off another Swedish giant by beating Malmo to earn their third win in four and climb to fourth in the table, while Malmo sit sixth having suffered a first defeat in four.
Things could have been different had Busanello's shot gone in off the post instead of bouncing clear off the upright in the fourth minute, yet instead the visitors found themselves a goal behind 10 minutes later when Axel Taonsa shrugged off his marker and buried a fierce strike into the bottom corner.
The Vasteras goal continued to live a charmed life as Daniel Gudjohnsen's shot was cleared off the line by Herman Magnusson, and in the second half, Taonsa was at it again when Jens Magnusson played him through and once more his effort was too powerful for Robin Olsen.
Taonsa was denied a hat-trick by the same post that thwarted Busanello, but the home side had done enough to move five points from the European places, even if the sides above them have a game in hand. MFF are two points further back.
Goteborg's second season of two halves in as many years has seen them move just eight points off the top three, as they needed just one goal to beat Brommapojkarna for a fourth win in a row, having picked up five in their first 18.
The goal arrived early in the second half, as Oliver Mansson looked to have been denied the shooting chance by a covering tackle, the ball fell kindly for Alexander Simmelhack, who made no mistake from close range for his second goal in three games since arriving from Silkeborg in Denmark.
Goteborg stay ninth, while it's successive defeats for the Bromma Boys, who sit in 11th place.