Magnus Carlsen’s career is in crisis and this week Norway’s 26-year-old world champion has been on the brink of losing the No1 ranking he has held without a break for almost six years.

Carlsen was in joint last place in the Altibox Norway elite event at Stavanger, with a pack of eager rivals within one game of usurping his No1 position, but he was saved, at least for the moment, when his old rival, Russia’s Sergey Karjakin, blundered a drawn position in Thursday’s penultimate round to give the beleaguered champion a windfall point. Carlsen then drew with India’s Vishy Anand in Friday’s ninth and final round to total 4/9 in next to last place with just a solitary win, six draws and two defeats.

After seven of the nine rounds Carlsen had not won a game, giving a drab performance and losing twice to major rivals. Levon Aronian beat him in a truly brilliant game with a sophisticated version of the ancient Greek Gift bishop sacrifice, then Russia’s former champion Vlad Kramnik also saw further than Carlsen in a tactical sequence.

Carlsen has often said he values being top of the rankings even more than his official world crown and at his zenith in July 2014 his rating was an all-time record of 2882, 50 points ahead of his nearest rival. Since then he has suffered some losses to weaker players as well as an increased ratio of draws.

His rating gradually dropped some 70 points and he retains the No1 spot only due to his earlier achievements. Taken alone, his 2017 results would put him outside the top 10. The live ratings after his win on Thursday show him at 2823 with five rivals, including the rampant Aronian, above 2800 and thus within striking distance.

Final scores from Stavanger were Levon Aronian (Armenia) 6/9, Hikaru Nakamura (US) and Vlad Kramnik (Russia) 5, Wesley So and Fabiano Caruana (both US) and Anish Giri (Netherlands) 4.5, Magnus Carlsen (Norway), Maxime Vachier-Lagrave (France) and Vishy Anand (India) 4, Sergey Karjakin (Russia) 3.5.

Exactly why Carlsen, who was widely expected to prove himself alongside Bobby Fischer and Garry Kasparov as one of the greatest world champions, is having such a prolonged slump in form is unclear. A grandmaster in his mid-20s is normally near his playing peak, because his ambition, creative energy and physical stamina for long games are all in good shape.

Carlsen’s special skill used to be to take on a long endgame with little or no advantage and grind the opponent down by incessant pressure. His opponents have got wise to that and more of his games now feature level positions where his well-prepared rival halves easily.

Kasparov thinks Carlsen’s play has stagnated and that his avoidance of mainstream opening theory blunts his edge. He spent weeks preparing for Stavanger, yet his repertoire included tame Italian openings. In contrast Aronian, who beat Carlsen brilliantly and won the tournament, came without a coach to help him prepare. The Armenian explained: “It is important to be responsible for your own preparation and to take it more seriously. You know, when there is no one to expect help from, you will be working more concentrated and determined.”

Aronian’s win from Carlsen was a remarkable mix of two classical tactical themes. He sacrificed first a pawn, then rook for bishop, to put the world champion’s queen in danger of being trapped. The pawn was a rook pawn, whereas in the Poisoned Pawn Sicilian, where Boris Spassky once famously beat Bobby Fischer, White gambits the b2 pawn.

Trying to rescue his queen, Carlsen left his king short of defenders and allowed a version of the Greek Gift bishop sacrifice. There were still mistakes on both sides until Aronian broke through to win one of the most original games of recent years.

The game showed that 11 a3! was a poisoned pawn, so Black’s safest was 11...Bd6 when White has just a small edge. Then 14...Ne4 set up the Greek Gift, where Aronian planned to meet 18...Kg6 by 19 Qg4 f5 20 Qg3 Kf6 21 d5! winning. As played, 25 Qa7?! (Qb7) gave Carlsen a possible escape by Nf6! but the world champion missed both that and 31...Rf8! which would have held on. These are small blemishes, though, in a classic victory.

Levon Aronian v Magnus Carlsen

1 d4 d5 2 c4 c6 3 Nf3 Nf6 4 Nc3 e6 5 e3 a6 6 b3 Bb4 7 Bd2 Nbd7 8 Bd3 O-O 9 O-O Qe7 10 Bc2! Rd8 11 a3! Bxa3?! 12 Rxa3! Qxa3 13 c5 b6 14 b4 Ne4?! 15 Nxe4 dxe4 16 Bxe4 Rb8 17 Bxh7+! Kxh7 18 Ng5+ Kg8 19 Qh5 Nf6 20 Qxf7+ Kh8 21 Qc7 Bd7 22 Nf7+ Kh7 23 Nxd8 Rc8 24 Qxb6 Nd5 25 Qa7 Rxd8 26 e4 Qd3? 27 exd5 Qxd2 28 Qc7! Qg5 29 dxc6?! Bc8 30 h3 Qd5 31 Rd1 e5? 32 Rd3 exd4 33 Qe7 Bf5 34 Rg3 Bg6 35 Qh4+ 1-0

3499 1 Rxg8+! Resigns. If 1...Kxg8 2 Rg4 and White’s queen easily defeats Black’s rook and bishop. If 1...Qxg8 2 Qf6! Bc5 3 Rg4 Qh7 4 d6 (threat 5 Qe7 mate) Re8 5 d7 wins.