Firm export numbers helped corn beat early blues to stand nearly 2% higher in late trade in Chicago, dragging corn and soybeans up with it.
External markets faded as the day wore on. While London's FTSE share index managed to match its record of 11 successive winning days, poor results from the likes of Aetna, the health insurer, and telecoms group Verizon Communications softened US stocks.
That took the wind out of oil's sails, with New York crude but $0.09 higher at $69.14 a barrel at 18:00 GMT, below a day high of $68.99 a barrel.
Still, Chicago commodities did their best to show decoupling from other markets, helped by US export inspections for corn of 52.2m bushels, way ahead of traders' estimates of, at best, 34m bushels.
The prospect of enthusiastic demand helped the crop dispel investors' lingering concerns over favourable weather to add 5.5 cents to $3.23 ¾ a bushel for the September contract.
That helped other crops out of a hole too, with wheat up 5 cents at $5.20 ¼ a bushel for September delivery despite weak export inspections of 10.7m bushels. The market had been looking for at least 14m bushels.
Soybeans for August were 0.5 cents lower at $10.22 a bushel.
Among softs, sugar again managed a three-year high – although less convincingly this time.
India's government, facing the prospect of relying on foreign shipments for a second year, has agreed to extend beyond this month a period of duty-free imports of raw and refined sugar, according to Reuters, the news agency.
In theory, that should have been excellent news for the market. But, as the old adage goes, buy on rumour, sell on fact.
New York sugar for October crawled 0.04 cents higher to 18.47 cents a pound.
Elsewhere, New York cocoa for September dropped $27 to $2,880 a tonne, with profit taking blamed for the commodity being unable to hold on to an 11-month high of $2,935 a tonne.
Its London counterpart ended down £34 at £1,807 a tonne.
But Chicago hogs recovered from early lows to avoid repeating Friday's 3% drops, which were blamed on weak pork prices and high animal weights.
August hogs stood 0.125 cents higher at 59.175 cents a pound.