user2429: I am reminded of a famous game between Karpov and Tony Miles where Miles played 1...a6 against Karpov's 1. e4 and still won the game. 
     [FEN "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1"]
     [White "Anatoly Karpov"]
     [Black "Tony Miles"]

     1...a6?!

Which other players in chess history have used dubious openings successfully? Which were the openings? 
NOTE: For the purpose of this question, the player (or the opponent) must either have been a world champion (like Karpov in this game) at some point or at least a strong contender for the world title during his time. Also, the openings must have been considered to be dubious during their time. 

user-1: Preston Ware is a 19th century American Chess master who played the Ware Opening/Meadow Hay Opening (1. a4) and the Corn Stalk Defence (1. e4 a5).

user1485: Thomas Wilson Barnes used 1. e4 f6?! to beat Paul Morphy.
   [FEN ""]  
   [Event "London m1"]
   [Site "London"]
   [Date "1858"]
   [Result "0-1"]
   [White "Paul Morphy"]
   [Black "Thomas Wilson Barnes"]
   [ECO "A00"]
   [PlyCount "100"]

  1.e4 f6 2.d4 e6 3.Bd3 Ne7 4.Be3 d5 5.Nc3 dxe4 6.Nxe4 Nd5 7.Nh3 Be7 8.Qh5+ g6 9.Qh6 Bf8 10.Qh4 Bg7 11.O-O O-O 12.c4 Nxe3 13.fxe3 f5 14.Neg5 h6 15.Nf3 e5 16.Qxd8 Rxd8 17.Bc2 exd4 18.exd4 Bxd4+ 19.Nxd4 Rxd4 20.Rfe1 Kf7 21.c5 Be6 22.Rad1 Nc6 23.Rxd4 Nxd4 24.Ba4 g5 25.Rd1 Rd8 26.a3 f4 27.Nf2 Ne2+ 28.Kf1 Rxd1+ 29.Bxd1 Nd4 30.Ke1 Kf6 31.Kd2 Nb3+ 32.Bxb3 Bxb3 33.Ng4+ Kg6 34.g3 h5 35.Nf2 Kf5 36.Kc3 Bd5 37.Kd4 c6 38.b4 Bg2 39.gxf4 Kxf4 40.a4 Bf1 41.Ne4 h4 42.Nd2 Be2 43.Ne4 g4 44.Nf2 Kf3 45.Ne4 Bf1 46.Ke5 Bd3 47.Ng5+ Kg2 48.Kd6 Kxh2 49.Kc7 Kg3 50.Kxb7 h3 0-1


user2429: Among World Champions, Alekhine was a top bluffmaster. Capablanca once remarked that "Alekhine's game is 20% bluff". 
Here's one example of his bluffs. 
    [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
    [White "Alekhine"]
    [Black "Erich Cohn"]

    1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Nxd4 Nf6 5. e5?

This was played in Alekhine vs Erich Cohn and Alekhine won that game. 
On one occasion, Magnus Carlsen himself played the shocking 1.a4 against a player as strong as Radjabov and still won the game. Although it was a blitz game, it was the World Blitz Championship 2012, so clearly not an ordinary event! Clearly, he managed to psychologically upset Radjabov.
    [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
    [White "Magnus Carlsen"]
    [Black "Teimour Radjabov"]

    1. a4 e5 2. e4 Nf6 3. Nc3 Nc6 4. Nf3 Bb4 5. Bb5 O-O 6. O-O d6 7. d3 Bg4 
    8. Ne2 a6 9. Bxc6 bxc6 10. Ng3 Nh5 11. h3 Nxg3 12. fxg3 Bd7 13. g4 Bc5 
    14. Kh1 Qe7 15. Qe1 f6 16. Nh4 g6 17. Bh6 Rf7 18. Rb1 Bb6 19. b3 d5 
    20. Nf3 Re8 21. Qg3 Bc5 22. Rbe1 dxe4 23. dxe4 Bd6 24. Re2 c5 
    25. Nd2 Be6 26. Qd3 g5 27. Qxa6 Kh8 28. Nc4 Bxc4 29. Qxc4 Rg8 
    30. h4 gxh4 31. g5 Rg6 32. Ref2


user291: If you really mean "dubious", then no one really fits this description since Steinitz, who liked to, for example, go for walks with his King when playing the King's Gambit as White. But people didn't really know better back then.
If you're willing to relax "dubious" to "offbeat", the first player that comes to mind is Bent Larsen, one of the strongest players in the world in the 1960s and 1970s. He regularly played 1.f4 and 1.b3 (often known now as Larsen's Opening), and also helped revive the Bishop's Opening and the Philidor Defense. None of these were regarded particularly seriously by top-level players at the time that he adopted them.
Before that, players like Réti and Nimzowitsch developed hypermodern theory, in which players tried to control the center from afar instead of occupying it with their pawns. Some players regarded this strategy as dubious but it shortly became clear that it was perfectly legitimate.

2429: <p>I am reminded of a famous <a href="http://www.chessgames.com/perl/chessgame?gid=1068157">game</a> between Karpov and Tony Miles where Miles played <strong>1...a6</strong> against Karpov's <strong>1. e4</strong> and still won the game. </p>

<pre><code>     [FEN "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1"]
     [White "Anatoly Karpov"]
     [Black "Tony Miles"]

     1...a6?!
</code></pre>

<p>Which other players in chess history have used dubious openings successfully? Which were the openings? </p>

<p><strong>NOTE:</strong> For the purpose of this question, the player (or the opponent) must either have been a <strong>world champion</strong> (like Karpov in this game) at some point or at least a <strong>strong contender for the world title</strong> during his time. Also, the openings must have been considered to be dubious during <em>their</em> time. </p>
 -1: <p><a href="https://en.wikipedia.org/wiki/Preston_Ware" rel="nofollow noreferrer">Preston Ware</a> is a 19th century American Chess master who played the Ware Opening/Meadow Hay Opening (1. a4) and the Corn Stalk Defence (1. e4 a5).</p>
 1485: <p>Thomas Wilson Barnes used <code>1. e4 f6?!</code> to beat Paul Morphy.</p>

<pre><code>   [FEN ""]  
   [Event "London m1"]
   [Site "London"]
   [Date "1858"]
   [Result "0-1"]
   [White "Paul Morphy"]
   [Black "Thomas Wilson Barnes"]
   [ECO "A00"]
   [PlyCount "100"]

  1.e4 f6 2.d4 e6 3.Bd3 Ne7 4.Be3 d5 5.Nc3 dxe4 6.Nxe4 Nd5 7.Nh3 Be7 8.Qh5+ g6 9.Qh6 Bf8 10.Qh4 Bg7 11.O-O O-O 12.c4 Nxe3 13.fxe3 f5 14.Neg5 h6 15.Nf3 e5 16.Qxd8 Rxd8 17.Bc2 exd4 18.exd4 Bxd4+ 19.Nxd4 Rxd4 20.Rfe1 Kf7 21.c5 Be6 22.Rad1 Nc6 23.Rxd4 Nxd4 24.Ba4 g5 25.Rd1 Rd8 26.a3 f4 27.Nf2 Ne2+ 28.Kf1 Rxd1+ 29.Bxd1 Nd4 30.Ke1 Kf6 31.Kd2 Nb3+ 32.Bxb3 Bxb3 33.Ng4+ Kg6 34.g3 h5 35.Nf2 Kf5 36.Kc3 Bd5 37.Kd4 c6 38.b4 Bg2 39.gxf4 Kxf4 40.a4 Bf1 41.Ne4 h4 42.Nd2 Be2 43.Ne4 g4 44.Nf2 Kf3 45.Ne4 Bf1 46.Ke5 Bd3 47.Ng5+ Kg2 48.Kd6 Kxh2 49.Kc7 Kg3 50.Kxb7 h3 0-1
</code></pre>
 2429: <p>Among World Champions, Alekhine was a top bluffmaster. Capablanca once remarked that "<a href="http://www.youtube.com/watch?v=nuyMzb5_tlU" rel="noreferrer">Alekhine's game is 20% bluff</a>". </p>

<p>Here's one example of his bluffs. </p>

<pre><code>    [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
    [White "Alekhine"]
    [Black "Erich Cohn"]

    1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. Nxd4 Nf6 5. e5?
</code></pre>

<p>This was played in <a href="http://www.chessgames.com/perl/chessgame?gid=1011822" rel="noreferrer">Alekhine vs Erich Cohn</a> and Alekhine won that game. </p>

<p>On one occasion, Magnus Carlsen himself played the shocking <strong>1.a4</strong> against a player as strong as Radjabov and still won the game. Although it was a <a href="http://www.chessgames.com/perl/chessgame?gid=1671724" rel="noreferrer">blitz game</a>, it was the World Blitz Championship 2012, so clearly not an ordinary event! Clearly, he managed to psychologically upset Radjabov.</p>

<pre><code>    [FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]
    [White "Magnus Carlsen"]
    [Black "Teimour Radjabov"]

    1. a4 e5 2. e4 Nf6 3. Nc3 Nc6 4. Nf3 Bb4 5. Bb5 O-O 6. O-O d6 7. d3 Bg4 
    8. Ne2 a6 9. Bxc6 bxc6 10. Ng3 Nh5 11. h3 Nxg3 12. fxg3 Bd7 13. g4 Bc5 
    14. Kh1 Qe7 15. Qe1 f6 16. Nh4 g6 17. Bh6 Rf7 18. Rb1 Bb6 19. b3 d5 
    20. Nf3 Re8 21. Qg3 Bc5 22. Rbe1 dxe4 23. dxe4 Bd6 24. Re2 c5 
    25. Nd2 Be6 26. Qd3 g5 27. Qxa6 Kh8 28. Nc4 Bxc4 29. Qxc4 Rg8 
    30. h4 gxh4 31. g5 Rg6 32. Ref2
</code></pre>
 291: <p>If you really mean "dubious", then no one really fits this description since Steinitz, who liked to, for example, go for walks with his King when playing the King's Gambit as White. But people didn't really know better back then.</p>

<p>If you're willing to relax "dubious" to "offbeat", the first player that comes to mind is Bent Larsen, one of the strongest players in the world in the 1960s and 1970s. He regularly played 1.f4 and 1.b3 (often known now as Larsen's Opening), and also helped revive the Bishop's Opening and the Philidor Defense. None of these were regarded particularly seriously by top-level players at the time that he adopted them.</p>

<p>Before that, players like Réti and Nimzowitsch developed hypermodern theory, in which players tried to control the center from afar instead of occupying it with their pawns. Some players regarded this strategy as dubious but it shortly became clear that it was perfectly legitimate.</p>
