KEG: A spotty game full of errors in which both sides missed chances to win. Definitely not one of Mason's better efforts.
7...c6: Mortimer's 7. c4 was questionable (7. Nc3 looks best), but Mason's 7...c6 made Moritmer's move look good, and bungled up his development. 7...Nc6 was best.
8...f5: Moritmer's 8. Qc2 was inferior to 8. cxd5 or 8. Nc3. Mason should have begun developing his Queen-side with 8... Na6. After the text, Mortimer could have seized a significant advantage with 9. cxd5.
9...NxN: Mason should surely now have begun bringing out his Queen-side pieces with 9...Na6. Exchanging Knights only helped White, who should have responded 10. QxN rather than messing up his pawn structure with 10. bxN (as he did).
10...dxc4: This should have been a losing move. Mason yet again missed a chance to develop his Queen-side with 10...Na6. Had Mortimer followed up 11. Bxc4+ Kh8 properly, the game should have been his.
12. Rd1: Mortimer here missed the powerful advance 12. e6.
13. Rb1: Mortimer should have squelched Mason's Queen-side prospects with 13. a4. (Far batter than the text and far better than the Tournament Book's suggested 13. Bg5).
13...b5: Mason yet again failed to attend to his undeveloped Queen-side. He should have played 13...Nd7.
14. Bd3: Far inferior to 14. Bf1.
14...Qh5: Yet again, Mason should have started developing his Queen-side pieces with 14...Nd7 instead of this misguided Queen move.
15. c4: The beginning of a bad plan that ultimately bore fruit only because of Mason's later misplays. 15. Re1 was best.
16. c5: Continuing with his bad plan. 16. Nd4 was best.
17. Be3: Needlessly blocking the e-file. Mortimer should have played to break up Mason's Queen-side pawns with 17. a3.
18...Be6: Mason finally begins to bring out his Queen-side pieces, but chose the wrong candidate. 18...Na6 was best.
21. Qc4: The wrong spot for the Queen. He should have played 21. Qa4.
(To be continued).