Archibald was thrilled as a double from Lyle Taylor secured victory against the second-bottom Steelmen and took Thistle’s points tally to 38, sending them above Kilmarnock into eighth place.
But the Firhill boss believes they will need more than 40 points to ensure they are not yet dragged into a playoff position as the Scottish top flight gets set to split into two.
He said: “I’m absolutely delighted with the win. I don’t think it was much of a spectacle in the first half but in the second half we were the better team and probably deserved the victory.
“We go into the split with confidence and with a seven-point cushion.
“The way it works, we could play them again in our next game and that could make the gap between us 10 points or four points.
“But we’re in a good place. We have momentum and another clean sheet as well but we’ll need more than this.
“You see the threat Motherwell pose with their strikers so they’ll win again and so will Ross County, so we’ll need to go again.
“The clean sheet was pleasing and it came from our two centre-backs standing up to their threat because they’re difficult guys to play against.
“I think we’ll need more than 40 points to stay up, although our goal difference will help as well.
“But going above Kilmarnock makes this a good day, even though they have games in hand.”
Archibald singled out striker Taylor for praise after he endured a tough week following two bad misses in the goalless draw against Aberdeen.
He added: “He’s always a threat. He’s horrible to play against for any centre-half. He’s always on your shoulder and he was a pest all day.
“I’m delighted for him because he got a lot of press last week for his two sitters but he came back with two great goals and should have had three.”
Motherwell boss Ian Baraclough admitted that his side did not do enough to merit the points but also claimed that both of Thistle’s goals were offside.
He said: “Both goals were offside, having seen them. It wasn’t picked up by anybody – even our lads.
“The second one was possibly a yard offside, the first one was tighter to call. You hope to get a bit of help from the officials but if he hasn’t seen it, that’s fine.
“We weren’t good enough in the second half to go and win the game.”