The Lionesses had already secured their passage into the quarter finals of the European Championship but created a proper party atmosphere at St Mary's Stadium with a 5-0 win.
Goals from Fran Kirby, Beth Mead, an own goal and an Alessia Russo brace ensured that not only did Sarina Wiegman's side progress in top spot, but they also shattered the group stage record for most goals scored with a staggering 14 to their name.
With a last eight fixture against Spain or Denmark ahead of them on Wednesday night, England have plenty of time to focus ahead of what will be another massive clash for the Lionesses, however according to Sanderson, the side deserve real credit for their performance in Southampton.
Speaking on talkSPORT's live coverage, Sanderson said: "It's been absolutely fantastic.
"In the first half tonight it wasn't their best performance, but in the second half they were on a different level, they were really were.
"They rang the changes at half-time and I think it definitely worked.
"I've said it many times, you're going to need the whole squad during this tournament.
"Alessio Russo with the two goals, she'll be really disappointed not to get the third in the end, but it was a really good performance from England.
"Northern Ireland really tried. I've said it before and I don't say it in a patronising way, but there's only so much that Northern Ireland can do with not really any support from the football association.
"Hopefully this will show them where they need to be at because their fans have been fantastic."
Sanderson added: "For England, not conceding is a major factor. If I'm a centre forward and I don't need to contemplate conceding, it's easier to score goals.
"It was a brilliant performance from England. Really, really good. The fans loved it and we go through as group winners."