The Italian made the podium in each of the season's first three races in Qatar, Argentina and the United States to lead the championship standings by six points from Yamaha teammate Maverick Vinales.
"I would never have expected to come to Jerez as a leader of the championship," said 38-year-old veteran Rossi.
"I'm very happy because we managed to solve some of the problems we encountered during the winter tests and we are doing really good races."
Rossi has an incredible record at the Jerez circuit, winning nine times, including last season.
"This is the first European race and it‘s a circuit I really enjoy," said Rossi, whose last world title came in 2009.
He won the 125cc world crown and 250cc title before stepping up and taking MotoGP by storm.
"We have improved a lot in Austin since the first free practice and now it will be important to improve again in Jerez," Rossi added.
Vinales' dream start to life since replacing Jorge Lorenzo was brought to an abrupt halt as, after winning the first two races of the season, he crashed out at the Grand Prix of the Americas a fortnight ago.
"After the disappointing result in Austin I‘m happy that I didn‘t sustain any injuries," said the Spaniard.
"We also proved that we have the potential to fight for the victory at every race and this motivates me to arrive to Jerez even stronger than I was at the last GP."
Home favourite Marc Marquez is the main threat to the Yamahas and his victory in Austin brought the defending world champion to within 18 points of Rossi and up to third in the championship standings.
"Of course our win in Austin gave the whole team more confidence," said Marquez.
"Racing at home and in front of my fan club is always special."
Lorenzo's decision to leave Yamaha for Ducati has backfired massively in the early part of the season as he is languishing down in 13th in the championship and has been outshone by teammate Andrea Dovizioso.
And despite previous success in Jerez with three wins, neither Lorenzo nor Dovizioso are expecting to compete for the win this weekend.
"Jerez is one of my favourite tracks, I have excellent memories of it, and I’ve scored a number of wins there, but it’s also true to say that it’s not the most favourable track for Ducati," said Lorenzo.
Dovizioso is fourth in the world championship behind the Yamaha duo and Marquez having bagged Ducati's only podium so far this season in Qatar.
"Our balance sheet after the first three rounds of the season is not satisfactory enough because we thought we would be quicker this year," said Dovizioso.
"With the exception of the Qatar race it hasn’t been like this so far. Although the Jerez track is one of the toughest for me and Ducati, I will be fighting hard in Spain to try and get back onto the podium."