In Milanese service
After that, Savelli became himself a condottiero captain, entering the service of Gian Galeazzo Visconti, the ruler of Milan, in 1388. Visconti sent him to support his allies in central Italy, aiding Siena against Montepulciano and the company of John Hawkwood, which was in the pay of Florence. In 1389 he was in Perugia, to prop up the local pro-Visconti noble faction against the pro-Florentine commoners. In 1390 he besieged Agello, held by the commoners, and after open war broke out between Milan and Florence, employed his men in the Val di Chiana. His results were poor, however, and in October Visconti recalled him to Milan.
In 1391 Savelli was back in Siena to take over command of the city, which in March of the same year had accepted Milanese rule. He was not very successful in stopping Florentine raids in the area. In 1392 he joined the army of the Visconti commander Jacopo Del Verme, and fought in the Battle of Soncino.
In 1394, Savelli returned to Rome, where he allied himself with Giovanni Colonna, the lord of Palestrina. On 24 July 1394 the two men tried to stage a coup by riding to the Capitoline Hill, but the attempt failed to gain any support.
In September 1395 he attended the ceremony of investiture of Gian Galeazzo Visconti as Duke of Milan and imperial vicar. In 1396–97, along with other Visconti commanders, he was again active in Tuscany in the conflict against Florence (although war was not officially declared until 18 March 1397) and in propping up the pro-Visconti regime in Pisa. In summer 1397 he participated in the attempt to capture Mantua, and fought in the unsuccessful Battle of Governolo in August, before returning to Siena in autumn to resume the expeditions against Florence and to support Jacopo d'Appiano, the lord of Pisa. Nevertheless, in January–February 1398 he was arrested by d'Appiano, after Visconti agents tried to have the fortresses of Pisa and other Tuscan cities handed over.
In June 1402 he played a major role in the Visconti victory in the Battle of Casalecchio against Giovanni I Bentivoglio, the lord of Bologna and close ally of Florence. Following the death of Gian Galeazzo Visconti in September, Savelli entered the regency council under the duchess dowager, Caterina Visconti, but he clashed with the other members and left it soon after. In May 1403 he participated in the defence of Bologna against Florentine and Papal troops, and remained in the city after the conclusion of the Peace of Caledio in August 1403, supporting the local faction of the Maltraversi. In the same autumn, he fought in the suppression of the uprising of Asola.
