Mine is still from year 1, when I was playing Reinhardt on Anubis.
My team got wiped out in the corner, but our Zarya managed to Grav the entire team in the corner before the choke…
(Noticing all the variables and Calculating.)
I “earth shattered” the whole team and charged has fast I could to point B. Then put up my shield, and couldn’t help but grin as I captured the point alone. (Watching them try so hard to destroy my barrier in time at the end.)
Athena map intro dialogue
take two steps
“VICTORY”
And more recently defending on King’s Row. Entire other team crashed out and weren’t replaced. Team just sat at the payload area staring at each other for the entire remaining match time.
I had a QP match where we sat on a objective together for 45 minutes… just chilling and emoting.
We had a torb battle to the death to see who won… LMAOOO
Other than the QP back fill games where you log into a victory screen…
Probably a game where I joined a match as Ana… healed for zero dmg. Slept one target and won. Seriously the enemy team was throwing so bad they didn’t manage to hurt anyone on our team.
I’m sure we’ve all had games where the entire team rushes way too far ahead. You’re just sitting there thinking “Look at those fools, they’re going to get crushed” and then you ride the cart through the entire map.
Bastion. On the payload with all DPS team. No Barriers, no healers. I sat there in Turret form. I got no Medals for damage or kills. I didn’t get any kills and I only periodically fired for a max of 3 seconds.
My team where all the “Trouble” DPS heroes:
They did all the work. I just got the longest time on objective card.
I’ve had games against deranking stacks where we literally just had to walk on point, and then stand around waiting for the timer to run off.
I’ve also had games where my smurfs were so blue that I really did not need to lift a finger to help them.
But in an actual fair match? I’d have to give a shoutout to the team that just, like, forgot to kill me (Mercy) after killing the rest of my team, and all ran off to spawncamp, leaving the payload unattended, you know how it goes. I just figured I’d start pushing to try and take some of the pressure of our spawn. Anyway their tracer comes running back to stop me but she did her running in a straight line, easiest dinkdinkdink of my life. Just in the nick of time she rewinds to save herself… ends up 300 feet away again and watches helplessly as I push the cart home.
On Junkertown in a comp match the cart was mere inches away from the point and as zarya i somehow managed to lure the entire team to follow me around the curve and into the underpass and grav them all there only to hop on the cart with a genji that just arrived and win the game. The best part was the teammates yelling at me for not being on the cart and wasting my grav before they realized what just happend. only buttons i pressed were SHIFT and Q while taking my enemy team out for a walk.
ah yes those games in where absolutely no one wants to be on the payload… you do the Good guy thing and push it.
Funny enough you get punished for it as you get nearly no SR as the game thinks you under preformed for the round. Despite you know winning the game for your team.
i always wonder about that…like a backfill a minute before win or last 10 percent, or the payload almost at the last checkpoint with like 6 minutes left.
had to be a disconnection or the dude had an emergency IRL. why would you leave lol???
This was while I was still in Bronze. Low Bronze too (and in 2017, so still early days of the game!), so my simple act was in fact a stroke of genius to both the time and my situation…
In order to win the Ranked match, all we had to do was get one tick of Point A Volskaya, so I snuck around the back as Tracer and back-capped. GG. 
Probably an even better one was about a year after that, where my team was so much better than me that I was just standing on the King’s Row payload as Soldier. Didn’t have to move off it once!
I once had a round of KotH where we captured the hill and got to 50% before we even saw one enemy.
Also a couple of these:
I don’t think much can beat old level 3 Torb Turret while emoting on the payload.
But in more recent years, I’ve substituted to heal-aura Lucio with his DJ emote. Only “won” a game with that once though.
I am sure most the back fill wins are something like that .Bad internet or Real life issues like some one at your front door. But some times the person is just so bad and toxic them leaving is all the team needs to win.
Capping the point as Sombra before the minimum 1 tick change to 2CP.
QP game, was tired speed boosting our rein around and he kept getting in bad positions and shattered. Realized our widow was a masters player and was doing stuff. Switched to Mercy, forgot tanks existed, and pocketed her, EZ game
When I did literally nothing and won anyways because of the perfect matchmaking with no flaws.
It was a 2CP map (maybe Anubis). My team reached point A and I died, but they captured that point. I respawned at the start of the map (before point A). While I was walking, the rest of the team was fighting and capturing point B. We won before I could reach point B 
Junkertown the other day. My team was pushing the other team so far back, I was the only one on cart the whole round. Just sat there looking at my phone and occasionally moving around so I didn’t get AFK kicked.
Hanamura 2nd point attack
My team planned out this whole elaborate attack where we would force the enemy to split their attention to overwhelm them. Made sure to coordinate going in together and everything.
Reaper just accidentally ended up back capping.