He almost gave Nadal a bagel in 2013 MC Final and broke Nadal's MC consecutive streak. All things considered I regard that along with his 2021 RG win as his biggest achievements.
2011 for me. He had prime, healthy Nadal, for the only time in his career, absolutely clueless about how to beat someone on clay, and mentally beaten by the end of their Rome match. If he hadn’t been up against Federer’s best RG level ever, he would have beaten Nadal in the RG final and that win would have been miles and miles above his other 2 RG wins over him.