Stocks ended Thursday almost exactly where they started. The bond market did not

If you only looked at the closing numbers, Thursday was a non-event. The S&P 500 finished 1.90 points lower at 7,704.13, a change of less than 0.1%. The Nasdaq Composite rose 3.34 points to 26,939.37. The Dow Jones Industrial Average was the only major benchmark with a visible loss, down 161.61 points, or 0.3%, at 51,349.98, which left the blue-chip index at a one-week low.

The path to those numbers was anything but calm. Stocks spent the morning under pressure, swung to gains, gave them back and flipped direction again before the bell. Nearly every one of those turns lined up with a move in Treasury yields, and the yield moves in turn lined up with the price of crude oil.

A morning set by the bond market

The selling that started in government bonds on Wednesday carried straight into Thursday. The benchmark 10-year Treasury yield climbed to roughly 5.22% at its peak, a level last seen in 2007, and the 30-year bond yield pushed to about 5.50%, its highest since 2004. Late Wednesday the 10-year had been near 5.11%, so the move added about a tenth of a percentage point in less than a day before it eased back to finish the session near 5.2%.

Several things fed the move at once. Oil was rising again. Economic data kept surprising on the strong side: weekly jobless claims came in below forecasts and August new-home sales beat expectations, extending a run of firm readings that began with Wednesday's September business-activity surveys. And Federal Reserve officials sounded open to more tightening. New York Fed President John Williams said it would be "reasonable" to expect another rate increase before year-end, while Philadelphia Fed President Anna Paulson also pointed toward further tightening but described it as likely to be modest.

Barchart also flagged soft demand at the Treasury's auction of seven-year notes on Thursday afternoon, another sign that buyers want more yield before they commit to longer-dated government debt.

The midday reversal

Around the middle of the session, the pattern briefly broke. The 10-year yield fell from close to 5.17% to below 5.13% in roughly 20 minutes, and one of the most actively traded Brent crude contracts dropped sharply in the same window. Stocks jumped. The trigger, according to several market wraps, was reporting that U.S. and Iranian negotiators were discussing an arrangement that would reopen the Strait of Hormuz in exchange for easing sanctions.

The relief did not last. With no formal agreement announced, oil turned higher again and yields followed. Front-month Brent crude settled at $106.60 a barrel, up 3.4% on the day, and West Texas Intermediate finished at $94.61, a gain of more than 2.5%. That combination pulled equities back toward the flat line into the close.

The closing prints hid a session in which stocks were effectively trading as a derivative of oil and Treasury yields.

Where the pressure showed up

Under the calm index totals, the pain landed where rising borrowing costs usually do. Market wraps pointed to weakness in housing-related names, solar companies and small caps, all groups that depend on cheap financing or are valued on profits expected far in the future. Chipmakers and AI-infrastructure stocks also retreated as yields climbed, a reminder that the market's biggest growth theme is not immune to a higher discount rate.

Energy was the obvious counterweight, helped by crude's rebound, and communication services were also among the stronger sectors at midday. Gold did not benefit from the geopolitical headlines; spot prices traded below $4,300 an ounce for much of the day as the dollar and real yields firmed, and gold-mining stocks fell with the metal.

What the market carries into Friday

The tone for the next session will again be set outside the stock market. The markers traders are watching:

• Durable goods orders for August at 8:30 a.m. ET and the final September University of Michigan consumer-sentiment reading at 10:00 a.m. ET, including its inflation-expectations component.
• Whether the 10-year yield holds around the 5.2% area or retreats toward 5.1%, which would take some pressure off rate-sensitive stocks.
• Any confirmed progress, or collapse, in U.S.-Iran talks over the Strait of Hormuz, the single biggest swing factor for crude this week.
• Fed pricing ahead of the October meeting. Futures-implied odds of another quarter-point hike ranged from roughly two-in-three to above 75% during Thursday, depending on the hour and the source.

Thursday's lesson was that a flat close can conceal a lot of movement. As long as oil and long-term yields stay this volatile, the major indexes are likely to keep reacting to them minute by minute, whatever the closing numbers say.