AdrianP: A nice crisp tactical win by Stein.
Stein's 13 dxc5, 14 Nh2 and 15 Qf3 strike me as being an unusual approach to the closed Lopez, but I imagine that the thinking is, if you're going to open the d-file, you'd better get your Q off it a.s.a.p. and f3 is probably a good place for the Q.
16 ...g6?! strikes me as dubious, weakening the dark squares and, in particular, the N on f6, a point which Stein exploits in the coming combinations. I imagine Mecking already had in mind the Nd4!? idea and wanted to stop the N coming to f5... but it comes to f5 anyway!
20. Nf5! exploiting the fact that 20...gxf5? fails to 21. Qg3+ threatening mate on g7.
22. Rxe5, the smoke briefly clears, material is equal, but Stein has a strong attack.
23 ...Bxh6, hoping for 24. Qxf6 Qxg6 and Black is just about holding.
24. Ng4! exploiting the fact that the f6 Knight is pinned against the f7 pawn (24...Nxg4?? 25. Qxf7+ and Qxh7#)
(32. ...Kf8 Qd6!+ 33 Ke8 Rg8#)