George Baldock fired the Blades in front at Bramall Lane before goals from Oli McBurnie and Yan Dhanda earned the relegated Swans all three points.
Five months on and the pair meet again, in Wales, for a televised teatime kick-off with the Blades in the ascendancy.
Manager Chris Wilder’s team are second in the Championship, looking for a fifth successive league win, while the Swans are languishing down in 13th.
Midfielder Fleck has once again been a key figure for United as the Blades look for a second promotion in three seasons.
“Swansea played us on the first day of the season and beat us in a tight match,” he said. “I think we have come on a fair bit since then and, hopefully, we can get a positive result.
“I think it is there for everyone to see we have a far stronger squad than we did last time.
“We did well in our first season back in the Championship last year and have kicked on since then as a group. We are doing well right now, but we need to stay focused. The hard work and effort we have put in has got us to this point. The aim is to stay there as long as possible, try not to drop out.
“We were probably not expected to be where we are at the moment.”
Fleck, 27, signed from Coventry City in 2016 and is now firmly settled with his family in Sheffield.
“It’s a fantastic club,” he said. “When you sign a long-term contract you have to uproot everything, your family. It’s all or nothing. It’s pretty similar to Glasgow; some places are nice, some places are rough. I enjoy going out for a coffee with the boys, it’s nice.
“Where I live there’s a mix of Sheffield Wednesday and United fans. You can get a bit of stick, but I am used to that as a young boy growing up in Glasgow. It’s all fun and games. It’s probably a little bit easier, to be fair, but the banter is good.”