2?
Only Starstrukk could be classified as a "massive hit" and arguably because of Perry. DTM didn't even reach the top 20.
I don't think it was because of Katy Perry especially. Remember Thinking of You and Waking Up in Vegas flopped here, arguably Starstrukk and If We Ever Meet Again are her biggest hits here and she's just the featured artist on both
1. California Gurls (feat. Snoop Dogg) - Katy Perry (=)
2. OMG (feat. will.i.am) - Usher (=)
3. Airplanes (feat. Hayley Williams of Paramore) - B.o.B (+1)
4. Beautiful Day - Lee DeWyze (-1)
5. Your Love Is My Drug - Ke$ha (=)
6. Alejandro - Lady GaGa (=)
7. Bulletproof - La Roux (=)
8. Not Afraid - Eminem (+1)
9. Hallelujah (American Idol Studio Version) - Lee DeWyze (+5)
10. Up to the Mountain - Crystal Bowersox (-2)
11. Break Your Heart (feat. Ludacris) - Taio Cruz (=)
12. Undo It - Carrie Underwood (=)
13. Can't Be Tamed - Miley Cyrus (=)
14. Billionaire (feat. Bruno Mars) - Travie McCoy (+1)
15. Rock That Body - Black Eyed Peas (+1)
16. Hey, Soul Sister - Train (+3)
17. Falling Slowly (American Idol Studio Version) - Lee DeWyze & Crystal Bowersox (=)
18. Young Forever (feat. Mr. Hudson) - Jay-Z (=)
19. Poker Face (Glee Cast Version) [feat. Idina Menzel] - Glee Cast (+5)
20. Nothin' On You (feat. Bruno Mars) - B.o.B (=)
21. Find Your Love - Drake (=)
22. Eenie Meenie - Sean Kingston & Justin Bieber (=)
23. My First Kiss (feat. Ke$ha) - 3OH!3 (=)
24. Impossible - Shontelle (+1)
25. Need You Now - Lady Antebellum (+3)
26. If We Ever Meet Again (feat. Katy Perry) - Timbaland (+1)
27. In My Head - Jason Derülo (+3)
28. Cooler Than Me (Single Mix) - Mike Posner (+22)
29. Poker Face (Glee Cast Version) [feat. Idina Menzel] - Glee Cast (-5)
30. Baby - Justin Bieber & Ludacris (+2)
31. My Chick Bad - Ludacris & Nicki Minaj (+5)
32. Tik Tok - Ke$ha (+9)
33. Winner (feat. Justin Timberlake & T.I.) - Jamie Foxx (+1)
34. Breakeven (Falling to Pieces) - The Script (+1)
35. Pray for You - Jaron and The Long Road to Love (+2)
36. This Afternoon - Nickelback (+7)
37. I Made It (Cash Money Heroes) [feat. Birdman, Jay Sean & Lil Wayne] - Kevin Rudolf (+1)
38. Rude Boy - Rihanna (+2)
39. Bad Romance (Glee Cast Version) - Glee Cast (-13)
40. The Boxer (American Idol Studio Version) - Lee DeWyze (-11)
41. Telephone - Lady GaGa & Beyoncé (+3)
42. Bad Romance - Lady GaGa (=)
43. The House That Built Me - Miranda Lambert (-4)
44. Ridin' Solo - Jason Derülo (+1)
45. All I Do Is Win (feat. T-Pain, Ludacris, Snoop Dogg & Rick Ross) - DJ Khaled (+2)
46. I Gotta Feeling - Black Eyed Peas (+2)
47. Over - Drake (-1)
48. Haven't Met You Yet - Michael Bublé (+1)
49. Airplanes (feat. Hayley Williams of Paramore) - B.o.B (+4)
50. Imma Be - Black Eyed Peas (+4)
51. Lover, Lover - Jerrod Niemann (+1)
52. Whataya Want from Me - Adam Lambert (+4)
53. Beth (Glee Cast Version) - Glee Cast (-20)
54. Billionaire (feat. Bruno Mars) - Travie McCoy (+7)
55. All the Right Moves - OneRepublic (+20)
56. Everybody Hurts (American Idol Studio Version) - Lee DeWyze (-25)
57. American Honey - Lady Antebellum (+3)
58. Carry Out (feat. Justin Timberlake) - Timbaland (+9)
59. Solo - Iyaz (-1)
60. Poker Face - Lady GaGa (+4)
61. Gettin' Over You (feat. Fergie & LMFAO) - David Guetta & Chris Willis (+7)
62. Touchin On My - 3OH!3 (-3)
63. I Like It (feat. Pitbull) - Enrique Iglesias (+8)
64. Rain Is a Good Thing - Luke Bryan (+6)
65. Every Rose Has Its Thorn - Poison (-8)
66. Empire State of Mind (feat. Alicia Keys) - Jay-Z (+19)
67. Smile - Uncle Kracker (+6)
68. Blah Blah Blah (feat. 3OH!3) - Ke$ha (+11)
69. Water - Brad Paisley (+9)
70. Drop the World - Lil Wayne & Eminem (+4)
71. I Never Told You - Colbie Caillat (+1)
72. Jessie's Girl (Glee Cast Version) - Glee Cast (-9)
73. Simple Man (American Idol Studio Version) - Lee DeWyze (-7)
74. Lose My Mind (feat. Plies) - Young Jeezy (+6)
75. Gimmie That Girl - Joe Nichols (+1)
76. Me and Bobby McGee (American Idol Studio Version) - Crystal Bowersox (-14)
77. Un-thinkable (I'm Ready) - Alicia Keys (+4)
78. Hello Good Morning (feat. T.I.) - Diddy - Dirty Money (+4)
79. Somebody to Love - Justin Bieber (+5)
80. Black Velvet (American Idol Studio Version) - Crystal Bowersox (-25)
81. Beamer, Benz, or Bentley (feat. Juelz Santana) - Lloyd Banks (+2)
82. I Dreamed a Dream (Glee Cast Version) [feat. Idina Menzel] - Glee Cast (-17)
83. Dream On (Glee Cast Version) [feat. Neil Patrick Harris] - Glee Cast (-14)
84. Say Aah (feat. Fabolous) - Trey Songz (+6)
85. Naturally - Selena Gomez & The Scene (+4)
86. Leave Right Now (As Heard On American Idol Season 9) - Will Young (-35)
87. Young Forever (feat. Mr. Hudson) - Jay-Z (+7)
88. Love Like Crazy - Lee Brice (-2)
89. Paparazzi - Lady GaGa (-2)
90. Lil Freak (feat. Nicki Minaj) - Usher (+2)
91. Party In the U.S.A. - Miley Cyrus (+4)
92. Nightmare - Avenged Sevenfold (-4)
93. Just Dance - Lady GaGa & Colby O'Donis (+6)
94. Don't Stop Believin' - Journey (+8)
95. Not Afraid - Eminem (+3)
96. I'm Back - T.I. (=)
97. Animal - Neon Trees (-6)
98. Uprising - Muse (-1)
99. The Only Exception - Paramore (-6)
100. Single Ladies (Put a Ring On It) - Beyoncé (+8)
168. Empire State of Mind (Part II) Broken Down - Alicia Keys (+45)
187. Secrets - OneRepublic (+225)
201. Apologize - OneRepublic (+340)
239. Empire State of Mind (feat. Alicia Keys) - Jay-Z (+63)
319. Chelsea Dagger - The Fratellis (+111)
329. The Funeral - Band of Horses (+130)
379. Stop and Stare - OneRepublic (+348)
474. Little Lion Man - Mumford & Sons (+129)
496. All I Want to Do - Sugarland (+183)
I don't think it was because of Katy Perry especially. Remember Thinking of You and Waking Up in Vegas flopped here, arguably Starstrukk and If We Ever Meet Again are her biggest hits here and she's just the featured artist on both
I Kissed a Girl - #1
Hot N Cold - #4
Katy has had some fame there, which no doubt helped the singles she was featured on.
we will have to see how this does in he UK. They had 2 massive hits there I'm honestly expecting a #1
I'm making it my mission to make this song top 10. 
