Only on the pitch a handful of minutes, he was fed in by fellow sub Barry Moran. The pass was behind him but on the turn, he rifled home and seemed to have sealed the points for the visitors.
However, they were left hanging on, as Derry went route one and found a goal from Brian Óg McGilligan, powering on to a Terence O’Brien cross to punch home. There were suggestions that Emmett McGuckin got a touch on the ball on its way in but McGilligan made the telling contact.
That closed the gap to two and Derry turfed the ball in again in their final attack, but despite winning possession inside the square, no-one could get the shot off, and Mayo survived.
They scarcely deserved it. It was a decent game, all in. With the sun shining, it was a step out of dreary February football and a touch closer to the summer. Neither side looked to be quite at their championship tilt but they managed to entertain the 3,801 in Celtic Park rightly.
When Sweeney netted, the table-toppers led 2-12 to 0-13 after they’d been pushed to the pin of their collars through the second half.
Playing with the breeze, Derry fought gamely and produced their best display of the league. But every time they got a foothold, Mayo pushed them away.
The Oak Leafers built up a head of steam, led by the introduction of James Kielt, and hit four points on the spin to pull themselves level at 0-13 to 1-10.
But the next two scores crucially went to Pat Holmes’ and Noel Connelly’s side. Kevin McLoughlin’s searing pace took him away to rifle a point over before he pointed another free.
Derry reacted furiously to its award, as they did to a number of Ciaran Branagan’s decisions. Brian McIver certainly didn’t hold back in his scathing assessment of the Down referee’s performance.
He was sore on Derry in parts of the game but overall, the referee was just poor. His inconsistency marred the game. He doled out two black cards when the game was almost over — the second of them to James Kielt for dissent — but turned away various other offences over the opening 65 minutes.
Away from that, Mayo appeared to have learnt at least some of the lessons of the Tyrone defeat.
Derry planted Aidan McAlynn as a sweeper and Carlus McWilliams dropped back to double up. It wasn’t quite 15 men in their own half, but they did their best to make life difficult for Mayo, whose transition from defence to attack was fluid and sharp.
Mayo posted Aidan O’Shea inside again in the first half and he proved an able ball-winner, and notched two scores from play for himself before the break.
Assisted by the breeze, they punished Derry mistakes with a direct counter-attacking style. They were aided largely by a stroke of luck for their goal, mind.
Four times the ball hit the woodwork in Celtic Park. Four times it favoured Mayo, and knocked another hinge off the trapdoor to Division Two for Derry.
Cillian O’Connor, who got a tough test off Dermot McBride, ought to have pointed a routine 35-yard free. It came down off the post and fell right at the foot of Mark Ronaldson. To give him his dues, the Shrule-Glencorrib man reacted well to turn it into goal from six yards.
Derry’s luck was absent seconds before the interval. The Oak Leafers’ attacking performance was vastly improved from previous performances, and they worked an opening for Sean Leo McGoldrick. His left-footed effort fell short and Michael McIver got his fist to it at the far post, but his effort came back off the bar.
That ensured that Mayo led at the break, 1-7 to 0-6, but it was a fairly insignificant advantage given the strength of the breeze they’d enjoyed, not to mind a sun that troubled the eyes of Oak Leaf defenders in the opening 35.
The second period took a while to warm but Derry found their groove and got themselves level. But in the end, the absence of Fergal Doherty from their midfield told, as Mayo were able to win crucial ball at crucial times.
Sweeney’s goal was enough to keep them level with Cork and set them up for a Dublin side that need points just as much as Derry did.
With trips to Dublin and Monaghan to come, Brian McIver’s Derry’s hopes of survival are dangling by the thinnest of threads.
Scorers for Derry: B Heron 0-4 (0-2f, 0-2 45’), J Kielt 0-4 (0-3f), B Óg McGilligan 1-0, M Lynch 0-2f, M Craig, B Óg McAlary, T O’Brien 0-1 each.
Scorers for Mayo: M Ronaldson 1-2, C O’Connor 0-4 (0-3f), A O’Shea 0-3, M Sweeney 1-0, K McLoughlin 0-2 (0-1f), J Doherty 0-1
Subs for Derry: M McIver for McAlynn (31), J Kielt for McKinless (HT), E McGuckin for McAlary (48), T O’Brien for McWilliams (57), S Brady for Kielt (bc, 68).
Subs for Mayo: A Dillon for Forde (48), B Moran for Kirby (55), A Freeman for O’Connor (61), D Drake for Cafferky (61), M Sweeney for Ronaldson (black card, 65)
Referee: C Branagan (Down).