Two late goals fired Leeds back to the top of the Sky Bet Championship as they beat Yorkshire rivals Barnsley 2-0 in a full-blooded derby at Oakwell.
But first substitute Eddie Nketiah scored his fourth goal in six matches since joining Leeds on loan from Arsenal before Mateusz Klich sealed the three points with a penalty five minutes later to lift United above Swansea on goal difference.
The result means Leeds have won six consecutive away matches in all competitions for only the third time in their history, previously doing so in 1931 and 1963.
Amongst the late goals, the game was sadly marred by incidents involving fans from both sides and the stewards.
On the pitch, the chances flowed, initially after just three minutes when Patrick Bamford was denied by the outstretched right leg of Collins.
Casilla twice thwarted the Tykes, beating away a 15-yard left-foot drive from former Leeds striker Mallik Wilks, and then a close-range effort from Luke Thomas after he had played a one-two on the edge of the area with another former White in Barnsley captain Alex Mowatt.
The closing 10 minutes saw a host of opportunities, initially with Jamie Shackleton setting Bamford free, but Collins again kept the forward at bay.
Within a minute Pablo Hernandez blazed over the crossbar from 12 yards after being teed-up by Jack Harrison, before Mowatt sent Wilks clear in the box but his shot was across the face of Casilla's goal.
In the final minute, Leeds then came closest to breaking the deadlock at that stage, with Harrison smashing a point-blank shot against a post after Stuart Dallas had flicked on a Kalvin Phillips corner.
The openings continued after the break with Collins saving from Bamford for the third time 48 seconds after the restart, and then Casilla brilliantly tipping a stunning 22-yard left-foot curler from Jacob Brown over the crossbar.
Bamford finally had the ball in the net a minute later only for the offside flag to adjudge half-time substitute Helder Costa offside in collecting Ezgjan Alioski's slide-rule ball down the left wing.
After Wilks blazed a shot into the side-netting and Cauley Woodrow headed tamely into the grateful arms of Casilla, the Leeds goalkeeper then had to be quick off his line to further frustrate Wilks close in before beating away at full stretch a 30-yard piledriver from Woodrow.
Not to be outdone by Casilla, Collins beat away a thumping 16-yard half-volley from Dallas in the 74th minute.
But six minutes from time Nketiah, who had replaced Bamford in the 70th minute, sent a side-foot volley past Collins having latched onto a piercing free-kick from Phillips.
It was then left to Klich to stroke a cool penalty past Collins in the 89th minute after Nketiah had been brought down by former White Aapo Halme to leave Barnsley without a win in their last seven games in all competitions.