Mexico started their Group B campaign with a 3-1 victory over Guyana on Friday.
They were comfortable winners at the Azteca stadium, taking a 3-0 lead inside 51 minutes before defender Hector Moreno put through his own goal to give Guyana a consolation, but Hernandez feels his side should have been celebrating a much bigger margin of victory.
The Manchester United hitman told reporters: "The El Salvador match will be difficult, but we still have to think of the Guyana match because there are things to improve.
"We should have won by a wider margin. Even winning, drawing or losing, there are always things to improve."
El Tricolor have claimed convincing victories in their last two meetings with El Salvador, winning 5-0 and 4-1.
However, both those triumphs came on home soil and in their last trip to San Salvador, in a qualifier for the 2010 World Cup, Mexico were beaten 2-1.
That loss is not playing on coach Jose Manuel de la Torre's mind, though.
He said: "There's no fear about going to El Salvador, just the opposite, we've been planning for the game looking to get a good result."
Tuesday's other Group B match sees Costa Rica travel to Guyana, having been held 2-2 at home by El Salvador in their first game.
Costa Rica led 2-0 after just 15 minutes in that match before being pegged back, and coach Jorge Luis Pinto is expected to make a number of changes to his line-up for the visit to Georgetown.
Striker Oscar Rojas said: "We're aware of the big responsibility we have in this match.
"We cannot change anything from the El Salvador game but we can correct some mistakes against Guyana."
In Group A, the USA go to Guatemala looking to build on their opening 3-1 win over Antigua & Barbuda.
The Americans came up against a side happy to keep players behind the ball in that match, but forward Clint Dempsey thinks it will be a different story on Tuesday.
He told reporters: "(Antigua & Barbuda) really sat back. I don't think Guatemala are going to sit back at home, so I don't think we're going to have to deal with that problem. I think they're going to be on the front foot."
He added on www.ussoccer.com: "They're going to be playing with that confidence that they've got the whole stadium behind them, and I don't really see them being a team that's going to sit back at home during a World Cup qualifier. In that sense, we don't have to worry about them packing it in the back."
Also in Group A, Antigua & Barbuda meet Jamaica in St. John's.
In Group C, Canada and Panama will be looking to build on opening-day triumphs with they play host to Honduras and Cuba, respectively.
Canada coach Stephen Hart, whose side beat Cuba 1-0 last time out, is not expecting an easy time of it on Tuesday, though, telling Honduran newspaper La Tribuna: "Honduras are a very balanced team and are totally focused on beating us after they lost to Panama so it will be much more difficult than before."
After six rounds in this phase, the top two teams from each group go through to the final stage, to be played next year.
The top three sides then qualify directly for the 2014 World Cup, with the fourth-placed team facing a home-and-away play-off against a South American team.
adidas has added some color to the Predator line with this new colorway. Released on May 17. Be the first to own a pair.
Ajax has released their away soccer jersey for the 2013/14 season. Get in the Gear.
The new PUMA evoSPEED 1.2 FG. A great new soccer cleat with classic look and first time for PUMA to be on the cleat.
Bayern Munich are kings of Germany and hope to be crowned kings of Europe at Wembley later this month!
The Liverpool 2013/14 soccer jersey is available for pre-order. The Reds are eager to compete for silver next season.
The push for more color on their cleats, adidas has added the infrared colorway to the adiZero f50 Line.
Chelsea won the Europa League on Wednesday. The Blues defeated Benfica 2-1 on injury time goal from Ivanovic.
The Juventus jersey for the 2013/14 was released earlier this week. Be the first to wear the colors of the Old Lady.
One of the top soccer cleats for control the Nike CTR360 will not let you down on the field in tight spaces.
Borussia Dortmund hears Wembley Calling and are headed to London for the Champions League final.