The collaboration rules the chart for a second week. Plus, 'Dark Horse' becomes Katy Perry's milestone 10th No. 1 on the Digital Songs chart and tops On-Demand Songs

Pitbull and Ke$ha spend a second week at No. 1 on the Billboard Hot 100 with "Timber." Meanwhile, Katy Perry jumps into the top five with "Dark Horse" (featuring Juicy J), which also crowns the Digital Songs and On-Demand Songs charts.

It's Wednesday, so time for our weekly look at the numbers behind the Hot 100's top 10.

Pitbull's second Hot 100 No. 1 and Ke$ha's third leader remains atop the Hot 100 despite not ruling any of the Hot 100's three main component charts, Digital Songs, Radio Songs and Streaming Songs. (With this week marking the one-year anniversary of the launch of Streaming Songs, it's just the fifth week in which the Hot 100's top song doesn't rank atop one of the three tallies. The last such occurrence: June 15, when Macklemore & Ryan Lewis' "Can't Hold Us" spent its fifth and final week at No. 1 on the Hot 100, while Robin Thicke's "Blurred Lines," "Justin Timberlake's "Mirrors" and PSY's "Gangnam Style" crowned Digital Songs, Radio Songs and Streaming Songs, respectively.)

Still, the continued multi-platform success of "Timber" keeps the song atop the Hot 100. It falls 1-2 after four weeks in charge of Digital Songs with 227,000 downloads sold (down 25%), according to Nielsen SoundScan. It reaches a new peak on Radio Songs (5-3), gaining by 15% to 125 million all-format audience impressions, according to Nielsen BDS. On Streaming Songs, the track slips from its No. 2 highpoint to No. 3, although with a 3% gain to 5.4 million U.S. streams, according to BDS.

"Timber" concurrently spends a second week at No. 1 on the Hot Rap Songs chart.

Below "Timber" on the Hot 100, OneRepublic's "Counting Stars" places at No. 2 for a second week. "Stars" holds at No. 2 on Radio Songs for a fifth frame (144 million, up 4%); dips 3-4 on Digital Songs (185,000, down 22%); and bullets at No. 7 on Streaming Songs (4.4 million, up 9%). As previously reported, "Stars" takes over atop the mainstream top 40 radio-based Pop Songs chart this week.

In terms of overall Hot 100 chart points, "Timber" wins the top spot by an 8% margin over "Stars." Last week, "Timber" won by a similar 9% points difference.

Eminem's former four-week No. 1 "Monster," featuring Rihanna, holds at No. 3 on the Hot 100 but continues leading Radio Songs for a sixth week (147 million, up 2%). It stays at No. 5 on Digital Songs (162,000, down 27%) and falls 6-8 on Streaming Songs (4.1 million, down 3%). "Monster" posts an 11th week at No. 1 on the Hot R&B/Hip-Hop Songs chart.

Katy Perry climbs into the Hot 100's top five with "Dark Horse," featuring Juicy J (6-4), the third single from her former Billboard 200 No. 1 album "PRISM." "Horse" gallops fueled heavily by its 4-1 coronation on Digital Songs, where it charges by 6% to 243,000. The song is Perry's 10th No. 1 on Digital Songs, the second-best sum after Rihanna's 13. Eminem ranks third with nine Digital Songs toppers, followed by Britney Spears (seven) and Bruno Mars and Taylor Swift (six each).

"Horse" likewise ascends to the top of the subscription services-based On-Demand Songs chart, rising 5-1 (1.9 million, up 25%), a surge which grants the song the Hot 100's top Streaming Gainer nod. The cut is Perry's second leader on the list, following "Roar," which reigned for two weeks in September. On the Streaming Songs chart, "Horse" hikes 10-5 (4.8 million, up 33%).

"Horse" additionally races with the Hot 100's top Airplay Gainer award for a second week, barreling 18-11 on Radio Songs (70 million, up 36%).

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Rounding out the Hot 100's top five, A Great Big World and Christina Aguilera's "Say Something" holds at No. 5. The ballad bounds 9-4 on Streaming Songs (4.8 million, up 27%) and 13-12 on Radio Songs (70 million, up 14%), while backtracking 2-3 on Digital Songs (218,000, down 10%).

Passenger's "Let Her Go" reaches a new Hot 100 peak (7-6) and dethrones Lorde's "Royals" (4-7) on Hot Rock Songs, which the latter song had led for 19 weeks, marking the sales/airplay/streaming-based chart's third-longest command; Imagine Dragons' "Radioactive" dominated for 23 weeks, followed by Foo Fighters' "Rope" (20, in 2011, when Hot Rock Songs was solely airplay-based). "Go" bullets at No. 8 on Radio Songs (84 million, up 6%) and returns to its No. 9 peak on Streaming Songs (13-9; 3.9 million, up 8%). On Digital Songs, it remains at No. 6 (146,000, down 21%). The track's climb to No. 1 on Hot Rock Songs marks its latest milestone, as "Go" topped 14 rankings in Billboard's international charts menu in 2012-13.

Avicii's No. 4 hit "Wake Me Up!" holds at No. 8 on the Hot 100, while commanding the Hot Dance/Electronic Songs chart for a record-extending 19th week.

Imagine Dragons' No. 6-peaking "Demons" rebounds 10-9 on the Hot 100 and One Direction's fellow No. 6 hit "Story of My Life" returns to the top 10 (12-10). Rising 15-14 on Radio Songs (69 million, up 22%, powered by its No. 8 rank on Pop Songs), "Life" has spent all 11 of its Hot 100 chart weeks in the top 15.

Just outside the Hot 100's top 10, Lorde's "Team" (14-11) and Bastille's "Pompeii" (18-12) could challenge for top 10 spots next week. Also next week: watch for Shakira's "Can't Remember to Forget You," featuring Rihanna, to enter the Hot 100 following its arrival at radio and retail on Monday (Jan. 13).

Visit Billboard.com tomorrow (Jan. 16), when all rankings, including the Hot 100 in its entirety and Digital Songs, Radio Songs, Streaming Songs and On-Demand Songs, will refresh, as they do each Thursday. The latest charts will also appear in the next issue of Billboard magazine (on sale on Friday, Jan. 17).