Derulo's first single Whatcha Say, debuted and peaked at number three last November, with first-week sales of 66,737, which have since swollen to 313,517. Both songs are on Derulo's eponymous debut album, which drops today (Monday).
Derulo's coronation is something of a Haiti handover - although born in Florida, the singer was born Jason Desrouleaux to Haitian parents, and his song replaces the Helping Haiti charity single Everybody Hurts, which takes a 1-9 tumble (33,084 sales) - the biggest for a number one single since McFly's Baby's Coming Back/Transylvania slumped 1-20 on May 26 2007.
In My Head is the third number one single in just three months to be produced and co-written by South African-born, Canadian raised Israeli Jonathan 'JR' Rotem, who performed the selfsame duties on JLS' Everybody In Love and Iyaz's Replay.
Derulo's number one debut was hard-earned - in early midweek flashes the Florence/Dizzee Rascal mash-up You Got The Dirtee Love was ahead but it eventually faded, and remains at number two on sales of 61,788 copies.
Meanwhile, although Sugababes' line-up has changed entirely since its 2000 debut Overload, the band notionally racks up its 26th hit - all of them Top 40, and 18 of them Top 10 entries - with Wear My Kiss, the third single from upcoming album Sweet 7, debuting at number seven on sales of 38,209 copies.
Three weeks after runner-up Marina & The Diamonds' Hollywood reached number 10, the winner of the BBC's Sound Of 2010 poll, Ellie Goulding, fares even better, debuting at number four with Starry Eyed (49,118 sales).
Singles sales fell 1% week-on-week to a new 2010 low of 2,886,214 but were still 16.78% above same week 2009 sales of 2,471,450.
44 weeks after completing a four-week stint atop the album chart, Lady GaGa's debut collection, The Fame, returns to the summit.
With GaGa currently on tour, and a trio of Brits awards under her belt, the album sold 45,358 copies last week, taking its 59-week career sales tally to 1,647,314. It has spent 40 of those weeks in the Top 10. The last regular (not hits) album to return to number one further into its chart career was David Gray's White Ladder, which improved 2-1 on 25 August 2001, its 68th week on the chart, having made it to the summit for the first time on week 66.
There were two more new Glee Cast releases this week - Sweet Caroline and The Thong Song. The former makes the Top 75 debuting at numbers 59 (4,914 sales) but the latter falls well short, entering at number 99 (2,542). Their album Glee: The Music - Season One, Volume 1 slips to number two (40,740 sales), having jumped 68-1 last week.
While first hit single Hollywood rallying 22-13, Sound Of 2010 runner-up Marina & The Diamonds makes a strong introductory showing on the album list, earning a number five debut on sales of 27,618 copies.
Manchester indie rockers The Courteeners returned to the singles chart for the first time since 2008, with You Overdid It Doll debuting at number 28 last week. That song now slides to number 44 (7,085 sales) but the group's second album, Falcon, fares better, snaring a number six debut (23,667 sales).
With the Brit effect waning, album sales were off 5.2% week-on-week at 1,925,786 - 0.85% above same week 2009 sales of 1,909,629.