MNb wrote on 10/03/07 at 02:15:18:

You're prolly right, but he was the first to really take the defense to a gambit to a new level. He faced and beat the likes of Chigorin, Blackburn and Steinitz (and numerous others) with all their gambits and tricky lines.

JEH wrote on 10/02/07 at 18:10:34:

Yes this one (Austrian attack with c5 but without the forced drawing line) is great 

I have thought of this, but the problem is that this anti-gambit idea is not really Lasker's.
I know of course, that 4.b4 Bxb4 5.c3 Ba5 6.0-0 d6 7.d4 Bb6 is called Lasker's Defence. The sequence 8.dxe5 dxe5 9.Qb3 Qf6 is known since Morphy's days. Lasker's untested contribution was 9.Qxd8 Nxd8 10.Nxe5 Nf6, but even that does not say much. Pillsbury's 10...Be6 is at least as good. To make things worse, Charousek's 7...Bd7 is probably superior to 7...Bb6. Finally Lasker had nothing to do with 6.d4 d6 nor 6.d4 exd4 7.0-0 Nge7. To summarize: Lasker's contribution to put the Evans out of business was restricted to a disputable innovation in a sideline of a variation, that might not be best for neither Black nor White, based on an idea that was not his own but Pillsbury's. And all this already was known before Lasker wrote his famous book. (Source: Botterill, Open Gambits 1985).
Lasker's 9...d5 10.Ba3 dxc4 is more important, but came in a time that only Steinitz was foolhardy enough to play the Greco Gambit 7.Nc3. Between Greco and Steinitz there is only one Harrwitz game. Not really hot theory.
It is not that I want to tear down Lasker's reputation, maybe the strongest player of all time. Still the concept of returning the gambit pawn for positional gains was also known before Lasker was born. See Rosanes-Anderssen, Breslau 1863: 1.e4 e5 2.f4 exf4 3.Nf3 g5 4.h4 g4 5.Ne5 Nf6 6.Bc4 d5 and Riemann-Anderssen, Breslau 1876: 1.e4 e5 2.f4 exf4 3.Bc4 Qh4+ 4.Kf1 d5 5.Bxd5 Nf6. Lasker was just the first to write it down. For this he deserves eternal gratitude from patzers like us, but no, not one of the greatest opening ideas.

MNb wrote on 10/02/07 at 21:52:45:

If you want a real concept, take Lasker's anti-gambit openings. He basically put the Evans, Greco and whatever open gambit out of business. Not just for a few years, but until now. He took the most dangerous lines and showed how to defend. 
Dont be fooled btw, whatever lines current gambiteers are focusing on are not the lines of Lasker. He refuted the more promising lines, so they are focusing on others.

Rubinstein's and Schlechter's king's fianchetto against the Tarrasch. This opening has never fully recovered from this blow. The great thing about it, is that it not a strong single move, but a whole new concept.
Another great idea is Pachman's and Keres' idea to play 6.Bg5 and 7.f4 against the Najdorf. This has kept the strongest players of the world busy for almost four decades and still has not disappeared.
Finally we should not forget Sämisch, who came up with Be3, Qd2 and f3 against the fianchetto defences. Quite influencial, I would say.

Some opening discoveries can open up whole new tracts of opening theory as they can turn an evaluation of main variation on its head. e.g. in the Pirc c5 Austrian, the now "well known" forced draw line, one probably baulked at by amatuers, really opened the door for this system.

Here are a few that come to my mind

-I think the Hedgehog - the whole idea that Black can adopt what must have seemed like a very  passive setup back then and yet his position is full of such latent dynamism.

-The ressurection of the Berlin would be another one.

-The exchange Ruy Lopez that Fischer honed into a White weapon.

-I think the concept of the Bf4 QGD with opposite side castling. With White's weakened Q-Side, it must have seen crazy at the time.

-Or going way back, just the idea of the hypermoderns that you did not have to actually occupy the centre was revolutionary in its day.