MissScarlett: The <Times-Democrat> of Monday, January 22nd 1883, p.3, confirms, as suspected, James DeBenneville Seguin as the opponent.
<The following is the unfinished game of Saturday night between Mr. Steinitz and Mr. Seguin. As will be seen, and as Mr. Steinitz remarked, Mr. Seguin has the winning game.>
The given score, <40...QR to K3 41 Q to B5 R to K4>, indicates that <40...R3e6 41.Qc5
Re5>, not <40...R8e6 41.Qc5 R3e5>, is the correct finish.
The previous day's edition, p.15, revealed this was part of a 20-board simul in which Steinitz scored +18 -1 and this one, <unfinished at 12 o' clock, the hour for closing the club. Mr. Steinitz, in regard to this latter game said that Mr. Seguin, having a clear rook ahead, was sure of winning, but that he, Steinitz, did not feel justified in resigning.>
That day's <Daily Picayune>, p.6, named all(?) eighteen opponents, but I'll stick with the <Times>'s numbers. And, contra <zanzibar>, I don't feel justified in changing the result of this game to <undecided>.
I'll submit the score of the Steinitz loss (vs. Blanchard).