The Italian opened his campaign by winning in Qatar, but in the two races since then, his rivals have overtaken and pushed Bagnaia down to fifth in the standings.
Heading into the fourth round on Sunday, Jorge Martin, who rides for Ducati's satellite Pramac team, has a 21-point advantage over Enea Bastianini.
The Italian, who like compatriot Bagnaia rides a factory Ducati, leads a pack of five riders separated by 10 points.
Maverick Vinales, fresh from a dominating weekend for Aprilia in Austin is third.
Teenage sensation Pedro Acosta, in his rookie season for GasGas Tech3, is fourth, just ahead of Bagnaia. South African Brad Binder is sixth on a KTM.
Bastianini said it's time to attack.
"In the last two Grands Prix, we've been on the defensive," he said.
"Over the past two years, we've got two fantastic wins here in Spain, and I'm going to contend again for the top positions this weekend. With plenty of fast riders on the grid, it won't be easy."
On this season's first visit to Spain, a quartet of Spaniards are poised to challenge.
"The special thing for the Spanish riders is that it's the first race you have your crowd here. It's a big push from the back," said Vinales.
He said that while he has won at Jerez in lower categories he only has a second and third in MotoGP.
"I want the first trophy," he said. "In Austin we write history. We are doing a good job."
Martin said he was trying not to be distracted by his connection with the track where his parents saw the famous 1996 duel between Spaniard Alex Criville and Australian Mick Doohan.
"Winning is enough. It is quite difficult," said Martin, before adding: "To win here is something else. My dad and mum were coming here before I was born to watch Criville and Doohan."
'We were fast'
Acosta, 19, has finished on the podium in the last two races. He could break the record for youngest-ever winner set by Marc Marquez, at 20 years and 60 days in 2013.
Acosta, who lives on Spain's Mediterranean coast, said he was determined to keep his feet on the ground.
"I'm back every week at home and I see the fishermen and how is real life and how people are working hard."
Marquez has won three times at Jerez but at the start of the 2020 campaign crashed there, suffering the broken arm that derailed him for most of four seasons.
The six-time MotoGP world champion has not won since October 2021 in Emilia-Romagna.
In his first season since leaving Honda for Gresini Ducati, he is eighth in the standings. While he is still having problems staying upright, he has looked ominously quick.
After Austin, where he led before crashing out, he said he was "satisfied" because "we were fast".
