* Soy harvest slightly ahead of expectations
* Corn edges up to nearly 11-week high on spreads against soy
* Wheat ends flat, pressured by technical selling (Updates with closing U.S. prices)
By Rod Nickel
WINNIPEG, Manitoba, Oct 4 (Reuters) - Chicago soybean prices fell on Tuesday, snuffing out a three-session rally as an accelerating U.S. harvest shifted attention back toward the prospect of record production.
Corn edged higher, supported by short-covering in spread trades against soybeans, while wheat finished flat, held in check by technical selling and ample U.S. supplies.
Chicago Board of Trade's most-active November soybean contract fell 1.1 percent, or 9-1/2 cents, to $9.63-1/2 a bushel, after prices on Monday hit their highest point since Sept. 23.
The U.S. soybean harvest was 26 percent complete as of Sunday, ahead of the trade estimates' average of 25 percent but behind the five-year average of 27 percent, the U.S. Department of Agriculture (USDA) said after the market closed on Monday.
USDA also said 74 percent of U.S. soybeans were in good or excellent shape, up one percentage point from a week ago.
"When you see the crop condition rating going up really late in the season, it signifies that yields are coming in better than expected," said Bill Nelson, soybean and products analyst at Doane Advisory Services.
Soybeans faced further pressure from favorable overnight rains in northern Brazil, where planting is underway, Nelson said.
Also after Monday trading, brokerage INTL FCStone raised its estimate of the average U.S. 2016 soybean yield to a record 52.5 bushels per acre (bpa), from 50.1 in its previous monthly report.
U.S. soybean export prospects were boosted by news that Argentina will not reduce export taxes this year or next as previously promised.
Most active December corn added 2-1/4 cents or 0.6 percent to $3.48-1/4 a bushel after earlier reaching a nearly 11-week high of $3.49.
USDA said the U.S. corn harvest was 24 percent complete by Sunday, behind the trade estimates' average of 25 percent and the five-year average of 27 percent. It said the U.S. winter wheat crop was 43 percent planted, behind the five-year average of 45 percent and analysts' average expectation of 47 percent.
INTL FCStone trimmed its corn yield forecast marginally to 175.2 bushels per acre from its September figure of 175.6 bushels.
Chicago most active December wheat finished flat at $3.95-1/2 a bushel.
Wheat traders awaited the outcome of a tender by the government buyer in Egypt, which drew nine offers. (Additional reporting by Julie Ingwersen in Chicago, Naveen Thukral in Singapore and Gus Trompiz in Paris; Editing by Susan Thomas, Paul Simao and Bill Rigby)