Later analysis shows that I did in fact find a best move over-the-board that was not in Fritz 10's book (but which was not a novelty either), and that I only made one serious error, which was not caught by my opponent.
For the viewers just tuning in, the Cochrane Gambit is a piece gambit by White in the Petroff Defense. White gives up a knight for two pawns and an out-of-place black king. Let's take a look.
Nigel Galia (1373) -- Jeff Young (1321)
New York State Championship, U1500, round 6, 9/2/2013
1.e4 e5 2.Nf3 Nf6
This is the Petroff Defense.
3.Nxe5 d6 4.Nxf7 Kxf7
And this is the Cochrane Gambit.
The main theory move. 5.Nc3 is the alternative. 5.Bc4+ is not good, being well-answered by 5...d5 6.exd5 giving an additional pawn for an even better position after 6...Bd6 or 6...Qe8+.
Not considered favorably in existing theory. Fritz 10 book gives it a "?". But I question that, because of the followup move below. The queen, taking advantage of the square vacated by the king, gives an uncomfortable pin on e4, no longer protectable via d3. (The immediate 5...Nxe4 loses the knight after 6.Qh5+, leaving Black down a pawn.)
6.Nc3 d5 7.e5
The theoretical responses, all moves trying to protect or attack the e4 pawn. Of course that pawn remains pinned and thus vulnerable to the following indirect attack.
This is the followup I referred to above. It destroys White's center. I found this over-the-board, but in fairness it comes from the same idea in a similar line I studied years ago with help from former co-worker and local chess artist Michael Mockler: 6.Bc4+ Be6 7.Bd3 c5!
My opponent finds the right idea and I find the right response. I was proud of my decision-making on this move also. I felt the chess legs had really kicked in.
Here my opponent falters, and I keep pressing. Ahead in material, I am more than happy to trade off knights or queens if he wants. He needed to find 9.Ne2 both protecting d4 and breaking the pin on e5 (forcing Nd7 for black), but who wants to retreat, even if mutually, in a gambit?
In fairness, I did not even see the tactic, but it was obvious I had to retake, so I made this move quickly and thought on my opponent's time. For some reason he took extra time here, perhaps trying to decide between the fork and Qh5+. Basically I saw that Be6 would be solid for Black.
11.Qf3+ Kg8 12.Qxd5+ Be6 13.Qe4
The idea for White is obvious -- trade on c6 and then take on d4. And here I engaged in some bad chess thinking. I got locked in on the idea Bxc6 bxc6 without looking at the alternative recapture! And I thought I had to protect both c6 and d4 with my queen for some reason. The right idea for Black is to get rid of the c6 pin via a6, when after Bxc6 Qxc6 Qxd4 Qxc2 there is no imbalance of material loss either. But the move I choose maintains Black's edge also, so I should be happy with it:
13...Qd7 14.f4 Qd5
More accurate is Bd5.
Developing with a cheapo threat, which my opponent is having nothing of:
Here is the true blunder. Although not horrible, it along with Black's previous inaccuracies does turn a practically winning black edge into a White edge, if White finds the way.
Again Black is more than willing to trade down.
Again my chess instincts come through. I remember recognizing Qf2 as an error, and just needing to find the most accurate response, which I think I did.
My opponent throws in the towel, trading down. Bxf2 was more accurate for Black, because leaving the rooks on makes e5 completely vulnerable, but I was more than happy to force further trade-down in a won position.
20.Rxf2 Bxf2 21.Bxc6 bxc6
Even more towel throwing.
I saw the fork, a chance for even more material, a passed pawn, and took it. Plus it centralizes the bishop.
23.Rb1 Bxe5 24.Ba3
A cheapo try for mate on f8 with the rook, but I just have too many ways out of it.
The idea being 25.Rf1 c5. I think I had by this time found a cheapo of my own as well, realizing that with the bishop on d4, the other bishop could defend any threat to d3 by safely planting on f5 with protection via g6 if necessary from any Rf1 attack, because any g4 attempt to attack the "pinned" bishop allows mate after Be4+. To my opponent's credit, he did not fall for this.
25.Rd1 Bf5 26.Rf1 g6 27.Rd1 Kg7
And White resigns here. The rook h8 will now finally emerge and combine with the d3 pawn to devastating effect.
So, is 7...c5! in this line a novelty? No! See note 52 here for references to games played from 2002 through 2005 with this line. I suppose between the Petroff, let alone the Cochrane, being rarely-played high-level openings these days, and theoreticians focusing elsewhere, it takes a long time for results and analysis to filter up to established theory. On the plus side, us patzers can enjoy being on the bleeding edge of theory in the meantime. :-)