I don't disagree with the point you're trying to make, as I think players in this category have better odds of troubling Djokovic with their variety. But, I think it is worth noting that Djokovic "struggling" with anyone at this point is a relative term. The only guys mentioned that has a winning record against Djoker is Federer. None of them have a winning record against him since 2011. Here's how it breaks down: vs. Federer (13-16 overall, 7-3 since 2011, 3-2 in the last five, Djoker won the most recent) vs. Murray (11-7 overall, 7-4 since 2011, 3-2 in the last five, Djoker has won the last 3) vs. Haas (4-3 overall, 2-1 since 2011, 2-3 in the last five, Haas won last night) vs. Tomic (3-0 overall) - Tomic did beat Djokovic in an exhibition early this year, but he hasn't troubled Djokovic much in matches that count. (Djoker won 6-2, 3-6, 6-3, 7-5 @ 2011 Wimbledon; 6-3, 6-3 @ 2012 Rome; 6-2, 6-3 @ 2012 Toronto) vs. Dimitrov (2-0 overall) - I looked him up because he has a lot of variety in his game as well. He lost 6-3, 6-2 in Shanghai last year and then 7-6(4), 6-1 at Indian Wells a couple weeks ago. We saw a glimpse of it perhaps in that first set at IW. Tomic and Dimitrov aren't really applicable yet because they're just now starting to play at the tour level from week-to-week. But, if you look closer at the Haas matchup, the matches are usually competitive. Roland Garros (2006) - Djokovic won 7-5, 6-1, 7-6(4) Indian Wells (2009) - Djokovic won 6-2, 7-6(1) Halle (2009) - Haas won 6-3, 6-7(4), 6-1 Wimbledon (2009) - Haas won 7-5, 7-6(6), 4-6, 6-3 Toronto (2012) - Djokovic won 6-3, 3-6, 6-3 Shanghai (2012) - Djokovic won 6-3, 6-3 Miami (2013) - Haas won 6-2, 6-4 In terms of sets, Djokovic has won 11 sets to Haas' 7. And of course, although he wins more often, his matches with Federer and Murray are almost always tight, often going the distance and featuring a lot of TB's or 7-5 sets.