User blog comment:IamJakuhoRaikoben/Chapter 487: The Third Seal, Review./@comment-191.251.188.176-20160530214925/@comment-7418318-20160530221753

But Natsu didn't solo a Spriggan. It was a team-fight in which Lucy contributed quite heavily. Not to mention that Jacob was depicted as one of the physically weakest members of the group.

The only one to defeat a Spriggan completely on his own so far is Laxus and even that's not sure, depending on whether the Jutsu-Shiki was something that Laxus learned from Freed or a pre-prepared trap created by Freed and only used by Laxus.

I guess Jellal might count too, since nobody even touched Neinhart before the one-shot, but then Erza made that one-shot possible by getting rid of the "obstacles" (i.e. the Histoira copies) in the way, who surely wouldn't have let Jellal just go ahead and attack Neinhart just like that.

Technically not even Acnologia defeated Serena in a clean one-on-one since Serena did take some damage from the Wizard Saints. Not that those minor wounds mattered one bit for that "fight", but they were still there.