A rusty Stan Wawrinka suffered a straight-sets defeat to Steve Johnson on his return from injury in the first round of the Internazionali BNL d'Italia on Sunday.

The three-time grand slam champion has been out of action since a shock defeat to Ilya Ivashka in Marseille back in February as he continued to be troubled by a knee injury.

Wawrinka said he could "see the end of the tunnel", but would need to be patient ahead of his comeback in Rome and he was unable to hit the ground running, losing 6-4 6-4 to Johnson on day one of the tournament.

The Swiss made 30 unforced errors and was broken once in each set by American Johnson, brimming with confidence after defending his title in Houston last month.

Wawrinka, who has been practising with his former coach Magnus Norman, has also been suffering from a calf problem but it was mainly Johnson's powerful forehands that were causing the 33-year-old pain in the Eternal City.

Johnson produced a couple of thunderous forehands to break for a 5-4 lead and served out the set to love in assured fashion, Wawrinka producing the odd trademark one-handed backhand winner as he tried to find his feet.

The Californian was playing with a swagger, breaking again in the second set to go 4-3 up when Wawrinka made a mess of a straightforward volley at the net and the world number 25 made an early exit after thudding a forehand into the net from beyond the baseline.