The morning infantry fighting occurred on either side of the Chambersburg Pike, mostly on McPherson Ridge. To the south, the dominant features were Willoughby Run and Herbst Woods (sometimes called McPherson Woods, but they were the property of John Herbst). Brig. Gen. Lysander Cutler's Union brigade opposed Davis's brigade; three of Cutler's regiments were north of the Pike, two to the south. To the left of Cutler, Brig. Gen. Solomon Meredith's Iron Brigade opposed Archer.^[8]

Major General John Reynolds and two brigades of the Union First Corps infantry arrive and join the line along McPherson Ridge against increasing pressure from the roughly 13,500 advancing Confederates. One is the Iron Brigade, the other is the PA Bucktail Brigade. General Reynolds directed both brigades into position and placed guns from the Maine battery of Capt. James A. Hall where Calef's had stood earlier.^[9] While the general rode his horse along the east end of Herbst Woods, shouting "Forward men! Forward for God's sake, and drive those fellows out of the woods," he fell from his horse, killed instantly by a bullet striking him behind the ear. (Some historians believe Reynolds was felled by a sharpshooter, but it is more likely that he was killed by random shot in a volley of rifle fire directed at the 2nd Wisconsin.) Maj. Gen. Abner Doubleday assumed command of the I Corps.^[10]

On the right of the Union line, three regiments of Cutler's brigade were fired on by Davis's brigade before they could get into position on the ridge. Davis's line overlapped the right of Cutler's, making the Union position untenable, and Wadsworth ordered Cutler's regiments back to Seminary Ridge. The commander of the 147th New York, Lt. Col. Francis C. Miller, was shot before he could inform his troops of the withdrawal, and they remained to fight under heavy pressure until a second order came. In under 30 minutes, 45% of Gen. Cutler's 1,007 men became casualties, with the 147th losing 207 of its 380 officers and men.^[11] Some of Davis's victorious men turned toward the Union positions south of the railroad bed while others drove east toward Seminary Ridge. This defocused the Confederate effort north of the pike.^[12]