The 22-year-olds were a sensational transfer coup last week for the Premier League club, who bought them from Corinthians.
The Brazilian club is owned by investment group MSI, who had talks to buy West Ham last year which came to nothing.
"We want to challenge the big teams in this division and this is a route to do that," Pardew told a news conference at Upton Park.
"As a team manager I want to work with the best players in the world...I think these guys are going to take us forward.
"I thought it was a fantastic move for us, to take us to the next level -- let's accept it for what it is."
Dismissing speculation the pair would not stay long, Pardew said they would definitely not be leaving in the January transfer window and had signed four-year contracts.
Pardew hopes West Ham will do so well this season that the pair will stay with a club who were promoted from the second division in 2005 and reached last season's FA Cup final -- earning themselves a UEFA Cup place.
"We wouldn't be sitting here with these guys if we hadn't had great success previous to this," Pardew said.
Mascherano said: "For any South American player, and in this case Argentine, it is a dream to play in European football... This was a very important goal for us."
Highlighting the lure of the English top-flight, he said: "Everyone knows it's one of the most important leagues".
Tevez added: "West Ham made us a firm offer...the fact of playing in the Premier League was the other factor in coming here."
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