Care had failed to enhance his Lions chances in England colours last month after disappointing showings against Italy and Wales but he was back to his brilliant best at Sixways.
The 26-year-old scored twice and set two up more touchdowns as the English Champions secured a semi-final spot in the Aviva Premiership and O'Shea says he has the magic to trouble the Wallabies Down Under.
"Danny is an absolute magician. I can't believe that in Australia, on hard grounds, Danny Care is not someone you need in your squad," said O'Shea.
"(Lions assistant coach) Rob Howley was watching him on an individual basis so I was told and it would be difficult not to look at him.
"He was pretty gutted not to have gone over for a hat-trick after the biggest hole in the world opened up for him but he put Tom Williams over, put Mike Brown over and scored a couple.
"That's pretty typical Danny, he's a brilliant player for us.
"He's been brilliant all season and he shouldn't be judged on one or two games. He should be judged on the season and his season's been outstanding."
Care darted over from close-range late in the first half for Harlequins and scored an even better try with another sharp break to bag the bonus point eight minutes after the break.
Gatland is likely to pick three scrum-halves in his squad a week today, with Care seemingly battling it out with the likes of Mike Phillips, Ben Youngs, Conor Murray and Greig Laidlaw for one of those spots.