Manuel Pellegrini's spell in charge of Manchester City started with a defeat to South African side Supersport in the first match of the Premier League side's pre-season campaign.
The Chilean, 59, left Malaga to take over as Roberto Mancini's successor at the Etihad Stadium last month.
But second-half goals from Mame Niang and Kermit Erasmus ensured that Pellegrini, who fielded a different team in each half in Pretoria, began with a defeat in the Nelson Mandela Invitational match at Loftus Versfeld.
The 2012 Premier League champions are next in action when they face AmaZulu in Durban on Thursday.
City's Spain internationals David Silva and Jesus Navas, a new signing from Sevilla, are joining up with the squad in Hong Kong next week, while Argentina internationals Sergio Aguero and Pablo Zabaleta will link up with their team-mates in South Africa later this week.
Pellegrini has made it clear that Edin Dzeko has a future with the club but the Bosnian striker passed up two early openings at Loftus Versfeld, heading straight at Ronwen Williams from a cross from new signing Fernandinho.
Dzeko also shot straight at Williams after a poor throw out from the goalkeeper and Aleksander Kolarov prodded wide after swapping passes with Dzeko. Samir Nasri slid a ball through for Dzeko but he was twice denied by Williams.
George Maluleka also clipped a free-kick narrowly wide and only a fine sliding challenge from Vincent Kompany stopped Sameegh Doutie giving the South African side the lead.
Dzeko also glanced a header narrowly over the bar from a Nasri free-kick just before the interval.
Pellegrini changed his entire team at the break, with Yaya Toure and James Milner among those brought on.
But the home side took the lead 10 minutes into the second period when a cross from Innocent Mdledle was met by a towering header from Niang that beat Costel Pantilimon.
James Milner went close to pulling City level but his effort was blocked by Boalefa Pule after the England midfielder was played in by Alex Nimely and Ivory Coast midfielder Yaya Toure also drove well over the bar.
But Erasmus guided a low effort past Pantilimon after breaking on to a pass from Morne Nel to give Supersport a victory in what was also the first game in charge for their coach, Cavin Johnson.