Mine is #82 (+17) on the Hot 100 this week, and it has crossover appeal so maybe that? but if that's not allowed then I guess Blow.
Edit: Pretty Hurts is the obvious choice. It's been charting high on iTunes since release and is very pop and likable even though it's a bit generic
XO needs time

like many people have said before, Halo was released in January 2009 and didn't start smashing until April
Quote:
"Halo" debuted at number 93 in the US Billboard Hot 100 chart issue dated February 7, 2009. It peaked at number 5 in the chart issue dated May 23, 2009.
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XO debuted at #66, so it's actually off to a better start. And as it's been said before you have to treat these singles more like a second and third single rather then a lead, due to the release strategy, hence why I'm comparing it to Halo.