Cilic was definitely out of nowhere. He had made 1 major semi I believe (2010 AO) and wasn't really heard from at big events after that. By USO 2014 he was not seen as much of a contender at all.
DP was certainly seen as a contender at USO 2009 as he came in playing pretty well but I'd say his breakouts before that had been moderate, making RG semis and Montreal finals that year.
As I said above, it's depends on how you define "breakthrough," and I tend to lean towards when we became aware of them. Both were on the radar for a fair amount of time. They came up at around the same time. Remember when we referred to them as the "twin towers?" But Cilic stagnated more. However, they did both break through to a different level when they won a Major, and each did it by beating Roger, if you guys want to add that to the list. Then again, they haven't really done much to back it up. Del Potro has been terribly unfortunate with injuries, of course, but he's only been in one other Major final since. And while Cilic has been in 2 others since, he's still really inconsistent.
