zanzibar: Let me try commenting on this game again, being a little more careful than last time.
There is another game between these players, a draw, here:
Steinitz vs Owen, 1862 (1/2-1/2)
Lowenthal's tournament book, on p lv, contains this:
<THE GRAND WEEK
On Monday, the 30th June, the spacious saloon of St. James's Hall was thrown open to the members. The walls were decorated with the flags of all nations, four long rows of tables covered with green cloth occupied the centre; a platform at one end forming a separate apartment, being reserved for the Managing Committee. At an early hour the players in the Tournaments, and amateurs who had hitherto been scattered about London, began to congregate, and the room soon wore an animated appearance. On Messrs. Anderssen and Paulsen entering the lists for their contest in the Grand Tournament, the interest of the spectators became centered in the struggle between these two celebrated players. The game lasted four hours, and was won by Herr Anderssen, whose chances of obtaining the first prize were thus materially increased. Three other en counters took place in the Grand Tournament. Mr. Barnes won of Mr. V.Green; Mr. Owen defeated Mr. Steinitz, and Messrs. Dubois and Blackburne had a drawn game.>
Two pages later, on p lvii is mention of the next day - Tues, July 1st.
Thus I think it reasonalbe to assume the "Mr. Owen defeated Mr. Steinitz" is referring to the first day of THE GRAND WEEK, i.e. Monday, the 30th.
I'm not sure when the draw between these players occurred, but I don't think it was on the 30th, given that the game here matches the result reported by Lowenthal for that day.