With a 20th week at No. 1 on Billboard's Adult Contemporary chart, Bruno Mars' "Just the Way You Are" becomes the longest-reigning debut single in the list's almost 50-year history.

The song bests the career-opening commands of Colbie Caillat's "Bubbly" (2008) and Daniel Powter's "Bad Day" (2006), each of which spent 19 weeks at No. 1.

("Way" marks Mars' debut song as a lead artist and his first to reach the Adult Contemporary chart. He previously charted on the Billboard Hot 100 as a featured vocalist on B.o.B's "Nothin' on You" (No. 1, two weeks) and Travie McCoy's "Billionaire" (No. 4) last year).

Here is a look at the longest-leading debut singles since the AC survey launched the week of July 17, 1961:

Weeks at No. 1, Title, Artist, Year(s)
20 weeks, "Just the Way You Are," Bruno Mars, 2011
19 weeks, "Bubbly," Colbie Caillat, 2008
19 weeks, "Bad Day," Daniel Powter, 2006
18 weeks, "Lonely No More," Rob Thomas, 2005-06
18 weeks, "Heaven," Los Lonely Boys, 2004-05

Before it reached the AC summit the week of Feb. 5, "Way" led Radio Songs (seven weeks), Adult Pop Songs (five), the Hot 100 (four), Pop Songs (three) and Digital Songs (two).

As "Way" makes AC chart history, follow-up "Grenade" bullets at No. 11 (after topping the Hot 100 for four weeks) and latest single "The Lazy Song" debuts at No. 30 (a week after reaching No. 4 on the Hot 100).

Mars' debut album "Doo-Wops & Hooligans" debuted on the Billboard 200 at No. 3 the week of Oct. 23, 2010, and has spent its first 35 weeks in the chart's top 40. The set has sold 1.1 million copies, according to Nielsen SoundScan.

All charts will be refreshed Thursday (June 16) on Billboard.com.