Watson and Grint played teen couple Hermione Granger and Ron Weasley in the Harry Potter series and have beaten the 'steamiest' couple Robert Pattinson and Kristina Stewart to the top spot.
The financial magazine then compiled the list based on highest box office earnings for each on-screen duo, reports the New York Daily News.
Viggo Mortensen and Liv Tyler of 'Lord of the Rings', who played lovers Arwen and Aragon in three Tolkien epics, reportedly earned USD3 billion for the LOTR franchise.
And Keira Knightly and Orlando Bloom of 'Pirates of the Caribbean', earned USD2.7 billion at the box office, coming in third.
Back to the Twilight couple, Pattinson and Stewart managed to get USD1.8 billion for the 'Twilight' franchise since the first film debuted to massive success in 2008.
