The force of nearly 10,000 men under Lord Methuen detailed by Buller for the relief of Kimberley, advanced from De Aar and Orange River Bridge along the railway. At Belmont a body of Free Staters under Jacob Prinsloo was found strongly posted on the heights east of the line, and although reinforced by Delarey from Kimberley, it was unable to hold to its positions, and was compelled to retreat eastwards on November 23.
Prinsloo withdrew with his Free Staters across the border, but was persuaded by Delarey, who had fallen back on Graspan about eight miles N.E. of Belmont, to rejoin him; and a favourable position was occupied on a group of kopjes astride the railway, where on November 25 another battle was fought, in which the Naval Brigade suffered a loss of nearly half its strength. The enemy, though driven back, retreated in good order, as at Belmont two days previously, there being no cavalry available for effective pursuit. Methuen pushed on to Witkoplaagte.
The Boers were greatly discouraged by Belmont and Graspan, where, as at Talana and Elandslaagte, they had been ejected from strong kopje positions chosen by themselves. The moral was not lost upon Delarey, who determined to try whether a better stand could not be made in a river position, and selected the junction of the Modder and the Riet for the experiment. His idea was not so much to dispute the passage of the river as to use the deep channels as covered ways and as natural trenches from which the plain could be grazed by rifle fire. The Modder after approaching the Riet changes its direction abruptly three tunes above the junction, enclosing a diamond-shaped area which provided the Boers with a ready-made perimeter camp.
Methuen, thinking that the enemy would as before select the good kopje position which offered itself on Spytfontein halfway to Kimberley, determined to diverge from the railway with the greater part of his army and circling through Jacobsdaal, Brown's Drift and Abon's Dam to attack Spytfontein in flank, where he had little doubt that he would find the Boers in position; but Modder River, which he was inclined to believe was only held as an advanced post, must first be taken. Delarey had been joined by P. Cronje, who unperceived by Methuen's cavalry came in with a body of Transvaalers from Mafeking, and was in occupation of the loop between the rivers.
At sunrise on November 28 Methuen advanced from his camp at Witkoplaagte six miles south of the river. The fight began under misapprehensions on each side. Methuen believed that only the river bank above the railway bridge was held in force; while he was credited by his opponents with the intention of crossing the Riet River by Bosnian's Drift of which he did not know the existence.
Everything promised well for Delarey and Cronje, but they made little use of their opportunities. Methuen fought in the dark, and whenever the Fog of War lifted, found that the situation had changed. He attacked the Modder as the opening move of his flank march on a mythical position on Spytfontein and suddenly discovered before him, not a mere advanced post to be checked or masked, but an enemy holding a well-entrenched and defended front several miles in length. The maps at his disposal did not shew the extraordinary windings of the two rivers over part of the area on which he was engaged, and some of the reaches were only discovered when they tripped up the advancing troops. The result of a hard day's work, in which Methuen was wounded, was the capture of Rosmead, a village on the right bank below the railway bridge. The troops of the right attack did not succeed in crossing the river, and an attempt to work up the right bank from Rosmead failed. What effect the battle would have upon the situation, and whether on the whole it had been a success for Methuen, were not apparent at nightfall. The question was answered next morning when it was found that the Boers had retired to Jacobsdaal. Next day the British troops took up a position north of the river.
So far, the Kimberley relief force had done its work well. The obstacles in its way at Belmont, Graspan, and Modder River had been thrust aside, and it was now within two easy marches of its destination. It seemed therefore that in three days at the most, allowing one day for another battle, it would be reported to Buller as having finished its task: and had the necessity been urgent the relief could no doubt have been effected within that time. Kimberley, however, appeared able to take care of itself for a few weeks, and Methuen halted for twelve days at Modder River in order to receive supplies and reinforcements, and to strengthen his slender and vulnerable line of communication with the south. He still believed that the Boers would make their next stand at Spytfontein.
The Boers remained but a few days at Jacobsdaal. After a council of war at which Cronje declared himself in favour of remaining there as a menace to the British line of communication which would attract Methuen to the town, a movement which Methuen himself had had in mind; while Delarey advocated the taking up of a position between the Modder River and Kimberley; the plan of the latter was adopted and the Boer forces trekked northwards to Spytfontein. They found, however, that between Spytfontein and the river, the Magersfontein group of kopjes would afford excellent positions to Methuen from which Spytfontein could be attacked.