The remaining portion of the en echelon attack was the responsibility of Maj. Gen. Richard H. Anderson's division of A.P. Hill's Third Corps, and he attacked starting at about 6 p.m. with five brigades in line.

The brigades of Wilcox and Lang hit the front and right flank of Humphreys's line, dooming any chance for his division to maintain its position on the Emmitsburg Road and completing the collapse of the III Corps. Humphrey displayed considerable bravery during the attack, leading his men from horseback and forcing them to maintain good order during their withdrawal.

On Cemetery Ridge, Generals Meade and Hancock were scrambling to find reinforcements. Meade had sent virtually all of his available troops (including most of the XII Corps, who would be needed momentarily on Culp's Hill) to his left flank to counter Longstreet's assault, leaving the center of his line relatively weak. There was insufficient infantry on Cemetery Ridge and only a few artillery pieces, rallied from the debacle of the Peach Orchard by Lt. Col. Freeman McGilvery.^[90]

The long march from Seminary Ridge had left some of the Southern units disorganized, and their commanders paused momentarily at Plum Run to reorganize. Hancock led the II Corps brigade of Col. George L. Willard to meet Barksdale's brigade as it moved toward the ridge. Willard's New Yorkers drove the Mississippians back to Emmitsburg Road.

As Hancock rode north to find additional reinforcements, he saw Wilcox's brigade nearing the base of the ridge, aiming at a gap in the Union line. The timing was critical, and Hancock chose the only troops at hand, the men of the 1st Minnesota, Harrow's Brigade, of the 2nd Division of the II Corps. They were originally placed there to guard Thomas's U.S. Battery. He pointed to a Confederate flag over the advancing line and shouted to Col. William Colvill, "Advance, Colonel, and take those colors!" The 262 Minnesotans charged the Alabama brigade with bayonets fixed, and they blunted their advance at Plum Run but at horrible cost—215 casualties (82%), including 40 deaths or mortal wounds, one of the largest regimental single-action losses of the war. Despite overwhelming Confederate numbers, the small 1st Minnesota, with the support of Willard's brigade on their left, checked Wilcox's advance and the Alabamians were forced to withdraw.^[91]

The third Confederate brigade in line, under Ambrose Wright, crushed two regiments posted on the Emmitsburg Road north of the Codori farm, captured the guns of two batteries, and advanced toward a gap in the Union line just south of the Copse of Trees. Wright's Georgia brigade may have reached the crest of Cemetery Ridge and beyond.

Carnot Posey's brigade made slow progress and never crossed the Emmitsburg Road, despite protestations from Wright. William Mahone's brigade inexplicably never moved at all. Gen. Anderson sent a messenger with orders to Mahone to advance, but Mahone refused. Part of the blame for the failure of Wright's assault must lie with Anderson, who took little active part in directing his division in battle.^[92]