By Eric Kelsey

LOS ANGELES (Reuters) - R&B singer Bruno Mars grabbed the top spot on the Billboard 200 album chart on Wednesday for the first time after discounted online prices boosted sales of "Unorthodox Jukebox" some four months after its release.

Mars' album, which includes the hit "Locked Out of Heaven," sold 95,000 copies last week, according to figures from Nielsen SoundScan.

Industry magazine Billboard said 64,000 units of the album were digital downloads following a one-day sale of $1.99 on Amazon.com's MP3 site.

Atoms for Peace, the rock group fronted by Radiohead singer Thom Yorke, claimed the second spot with their debut album "Amok" entering the chart at No. 2, selling 50,000 units.

Mumford & Sons' Grammy-winning album "Babel" fell from the top spot last week into third, while the same Amazon MP3 online sale that helped Mars also vaulted hip-hop duo Macklemore & Ryan Lewis' album "The Heist" from No. 16 to No. 4.

Hillsong United, the band from Australian megachurch Hillsong, rounded out the top five with the album "Zion," selling 34,000 units in its first week.

Three of the top four albums are distributed by independent companies rather than large conglomerates, the first time it has happened since Nielsen SoundScan began tracking sales in 1991, Billboard said.

Alternative Distribution Alliance distributed albums for Atoms for Peace and Macklemore & Ryan Lewis. RED Distribution released "Babel" for Mumford & Sons.

On the digital songs chart, Macklemore & Ryan Lewis' cheeky rap "Thrift Shop" held at No. 1 for the eighth consecutive week with 326,000 downloads, a 10 percent decline from last week.

Mars' song "When I Was Your Man" placed second, trading spots from last week with viral music video hit "Harlem Shake" by electronic artist Baauer, who landed at No. 3 this week.

Digital song downloads totaled 253.8 million for the year, which is down 2 percent compared to the same period in 2012.

(Reporting by Eric Kelsey; Editing by Piya Sinha-Roy and Doina Chiacu)