Brighton produced an encouraging display but Foden's clever finish with his right foot just before the break was just too accurate for Albion keeper Robert Sanchez.
City deserved their victory and it could have been more for the hosts had it not been for a number of decent saves from Sanchez after the break.
Raheem Sterling also missed a penalty for City and Bernardo Silva had an effort crack back off the crossbar and Mahrez also wasted a glorious chance for Pep Guardiola's men just after the break.
But Brighton will be encouraged by the displays of debutant Percy Tau, while Leo Trossard and Alexis Mac Allister also performed well.
Scroll down and click through to see how they rated
1. Robert Sanchez 7/10
No chance with Foden's well placed finish. Made a good save from De Bruyne on 13 minutes. A bizarre choice to pick up a back pass from Webster but got away with it thanks to a good block from Mac Allister. Also denied De Bruyne on 40 minutes and also after the break.
2. Joel Veltman 6/10
Booked for a hefty challenge on Foden but a solid display as always from the Dutchman. Proved a very reliable summer signing from Ajax
3. Lewis Dunk 6/10
Would have been relieved that Aguero wasn't playing but still had to be alert against the considerable threat of De Bruyne and co. Did his defensive duties well as always
4. Adam Webster 7/10
Another very good display from the centre back. Drove forward when he could and defended with confidence. Booked for a foul on Silva.