When Taylor Swift's instant smash “Shake It Off” entered the Hot 100 at #1 two weeks ago, it looked like Meghan Trainor would have to be content with a #2 hit on her first try. Trainor’s charming, doo-wop shaded “All About That Bass,” which had been streaking up the chart, slipped from #2 to #3 that week. (It was pushed down not only by “Shake It Off” but also by Nicki Minaj's surging “Anaconda.”) But this week, in a pop chart equivalent of David and Goliath, the talented rookie unseats one of the biggest stars in the music business.

"Shake It Off" climbs to #1 in its ninth week. "Shake It Off" slips to #2 in its third week. (Consolation prize: Swift’s hit tops the 1 million mark in digital sales this week.)

This marks the second time this year that a female artist has reached #1 with her first Hot 100 single (as a lead artist). The same thing happened in June with Iggy Azalea's “Fancy” (which featured chart “sophomore” Charli XCX). Billboard’s Gary Trust notes that this is the first time that two female artists in lead roles have reached #1 with their initial Hot 100 hits since 2008, when both Leona Lewis (“Bleeding Love”) and Katy Perry (“I Kissed A Girl”) did it.

"All About That Bass," which focuses on the importance of a positive body image, is one of the biggest and best "message songs" of recent years. The video is sure to be a leading candidate for Best Video With A Social Message at next year’s VMAs. Over the past four years, the award has gone to Lady Gaga's “Born This Way,” Demi Lovato's “Skyscraper,” Macklemore & Ryan Lewis featuring Mary Lambert's “Same Love” and Beyonce's “Pretty Hurts.”

"All About That Bass" returns to #1 on Hot Digital Songs (312K) after being held out of the top spot the past two weeks by "Shake It Off." This is the song’s third week on top.

Female artists make a clean sweep of the top five positions on the Hot 100 for the first time in more than 2-1/2 years. Nicki Minaj's aforementioned “Anaconda” holds at #3 in its fifth week. “Bang Bang” by Jessie J, Ariana Grande & Nicki Minaj holds at #4 in its sixth week. “Black Widow” by Iggy Azalea featuring Rita Ora jumps from #6 to #5 in its 10th week.

This marks the first time that female artists have locked up the entire top five since the week ending Feb. 19, 2012. Katy Perry's “Part Of Me” debuted at #1 that week, followed by Adele's “Set Fire To The Rain,” Whitney Houston's “I Will Always Love You,” Kelly Clarkson's “Stronger (What Doesn't Kill You)” and Adele's “Rolling In The Deep.” (That was the first full week following both Houston's death and Adele's sweep of the Grammys).

Here are a few more details on these current hits: “Anaconda” holds at #1 on Hot R&B/Hip-Hop Songs for the third week. “Bang Bang” and “Black Widow” each top the 1 million mark in digital sales this week. Also, “Black Widow” becomes Azalea’s third top five hit on the Hot 100 so far this year. This puts her in a tie with Ariana Grande for the most top five hits by any artist so far this year.

The highest-ranking male artist on the Hot 100 is again Sam Smith, whose “Stay With Me” dips from #5 to #6 in its 22nd week. The song peaked at #2. It logs its fifth week at #1 on the Radio Songs chart.

MAGIC!'s “Rude” rebounds from #8 to #7 in its 20th week. The song spent six weeks at #1 … “Break Free” by Ariana Grande featuring Zedd dips from #7 to #8 in its 10th week. The song peaked at #4.

Maroon 5's “Maps” rebounds from #11 to #9 in its 12th week. The group lands its second #1 album this week with V. “Maps” has climbed as high as #6, which puts it in the middle of the pack in terms of lead singles from Maroon 5 albums. “Harder To Breathe,” the first single from their debut album, peaked at #18. “Makes Me Wonder,” the first single from their sophomore album, made #1. “Misery,” the first single from their third album, peaked at #14. “Payphone” (featuring Wiz Khalifa), the first single from their fourth album, reached #2.

Sia's “Chandelier” dips from #9 to #10 in its 18th week. It peaked at #8.

Charli XCX's “Boom Clap” drops out of the top 10—for the second time.

Florida Georgia Line's “Cruise” tops the 7 million mark in digital sales this week. It's the best-selling country hit in digital history. The song logged 24 weeks at #1 on Hot Country Songs, longer than any other song in the chart's 70-year history. A remix featuring Nelly reached #4 on the Hot 100.

"Problem" by Ariana Grande featuring Iggy Azalea tops the 3 million mark in digital sales this week. It logged five weeks at #2 on the Hot 100.

To My Readers: I’ll have a second Chart Watch blog drawn from the Hot 100 later today.

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