Magoffin took five wickets as Nottinghamshire amassed 447, mainky thanks to Riki Wessels' unbeaten 202, before Sussex ended on 11-3.
The fast bowler said: “It was a tough day for us to have them 88-5 at one stage. Credit to Riki, he’s played an absolutely outstanding innings there but we probably weren’t at our best. We’ve got to admit that and come back with the ball next time and put in a better performance.
"Tomorrow’s all about fighting hard and seeing how close we can get to their total and see where we’re situated at the end of the day.
"I’ve been struggling with my knee the last fortnight and I took the last game off to get myself the best chance possible to play here.
"We know the Notts team is a very good side and we wanted to give ourselves the best chance of playing here. It’s a ground I enjoy playing it but it’s pretty sore at the Moment. To put in 18 overs by an hour after lunch they kind of got the better of it, so I’ll try and look after it over the next day or so and hope to be able to go again in the second innings.”
Wessels said: "It’s quite nice to get to a double-hundred for the first time in my career. I probably should have done it all those years ago at Hove but I’m grateful today.
“It was only when Bally (last man Jake Ball) came out to bat that I started to think about a 200 and we spoke about it when we came off the first time for bad light but the first thing was to get to 400 to make sure they were on the back foot. That was the first objective but then Jake hung around a bit longer thankfully.
And Wessels was pleased when Magoffin was not in the attack. He said: “He’s done well for then for the last four or five years and always gets his 70-odd wickets, so we were happy when he wasn’t bowling.
“I really value my four day cricket. I think the championship is something special. I don’t play Test cricket so this is a close as I can get to emulating that, so I take it very seriously and really enjoy playing. It hurt a bit last year, there’s always younger, stronger, fitter players coming into it, that’s the way it goes.”