"I was in no man's land today. I had no pace so I was just trying to hold on for whatever I had," the Mercedes driver told reporters at the Chinese Grand Prix.
"I had the older tyre on and I was running out of it."
The Briton finished fifth on track but moved up to fourth after a 10 second penalty was applied to Red Bull's Max Verstappen.
That allowed him to cut Sebastian Vettel's overall lead from 17 points to nine, with the Ferrari driver finishing only eighth.
"Obviously it's a tough battle ahead of us. I would say on my side but also us as a team, we've been underperforming," said Hamilton.
"Yesterday and today have been a disaster on my side so I have got to try and rectify that and get myself back into normal performance mode, otherwise more valuable points will be lost," said Hamilton.
The Briton had also said in Bahrain last weekend, when he finished third after starting ninth, that he had felt he was driving around in no-man's land.
But he arrived in Shanghai with an envious record, winner an unprecedented five times at a Chinese circuit that has long favoured Mercedes.
Hamilton was never a force to reckon with this time, however, qualifying only fourth and losing a place immediately at the start.
With Red Bull's Daniel Ricciardo winning the race, champions Mercedes have now been beaten three races in a row for the first time in the V6 turbo hybrid era that started in 2014.
Hamilton could at least depend on his car's impressive reliability, collecting points for the 28th race in a row and claiming outright a record he had previously held jointly with Ferrari's Kimi Raikkonen.
(Writing by Alan Baldwin in London, editing by Toby Davis)
