(CNN) -- The saying goes that a bad workman blames his tools but Roger Federer refused to pin a shock defeat in Hamburg on his new racquet.
Federer, who is experimenting with a larger tennis racquet at the German tennis championships, was stunned in the semi-finals by qualifier Federico Delbonis, the world no. 114.
"He was better than me," said Federer, who lost a tight match 7-6 (9-7) 7-6 (7-4) to the Argentine. "I don't think it had much to do with the racquet.
"Both sets could have gone either way. It's clearly a pity I couldn't win either of the sets because I was starting to feel better towards the end of the match.
"Unfortunately I couldn't push him further and create more chances.
"I tried everything I could at this tournament. It's been a difficult week."
Federer entered the Hamburg clay-court tournament to try and rediscover some form after a dismal Wimbledon.
The Swiss winner of a record 17 grand slams made a shock second-round exit at the All England Club championships at the hands of 116th ranked Sergiy Stakhovsky.
Part of his plan to get back to his best has been a decision to play with a larger 98-inch square frame racquet -- eight inches larger than his previous racquet.
Explaining his decision to try out the racquet in Hamburg earlier this week, Federer said on the ATP Tour website: "I've been very close on numerous occasions to changing racquets in a bigger way.
"But then very often, time was the issue. Maybe also just the records of grand slams - I was always keeping on playing quarters and semis - so then it was also a bit more difficult to change it because of the time.
"After I lost at Wimbledon, I thought this is a good time to go and test the racquets, to take a bit of time off and then add some tournaments and see was there enough time to change or not.
"I'm happy I did the change and now we'll see how it goes."
Federer -- who dropped from third to fifth in the world rankings after his Wimbledon loss -- will now head home to Switzerland to play at Gstaad next week.
Delbonis now faces Fabio Fognini for the Hamburg title after the Italian beat Spain's Nicolas Almagro 6-4 7-6 (7-1).