Jahn, a supplemental pick by the San Jose Earthquakes last year, will play forward for the Earthquakes when they host the Los Angeles Galaxy at 7:30 p.m., in what is billed as the California Clasico. Fireworks are guaranteed.
The Earthquakes-Galaxy rivalry has been called the best in Major League Soccer and, if last year's game at Stanford that drew in excess of 50,000 fans is any indication, things could heat up quickly this weekend.
Jahn has been a pleasant surprise for the struggling Earthquakes (4-7-6), eighth in the nine-team Western Conference. Expected to spend the season as a backup, Jahn has been thrust into the starting lineup as a result of injuries to a few of San Jose's forwards, including reigning league MVP and top scorer Chris Wondolowski.
Wondolowski missed the Earthquakes' 1-0 loss to host DC United last weekend, a match that snapped DC's 13-game winless streak.
"Adam has been great," Earthquakes interim coach Mark Watson said. "We've seen him for a few years since he's been at Stanford. We brought him in with a view to development. He had to be patient for his opportunity. But things happened and he's gotten the opportunity to play and has been great."
Jahn, who scored 13 goals in 18 matches and was named first team All-Pac-12 Conference for the Cardinal last year, is the second-leading scorer for the Earthquakes, with four goals.
"I didn't expect to be playing much because there were so many good forwards here," Jahn said. "But there were some injuries and I got the chance. Playing has given me confidence and the willingness to get into this training."
Watson, who was named interim coach three weeks ago, looks at the California Clasico as a game that could change the Earthquakes' fortunes this year.
"We've had a tough season so far, that's obvious," said Watson, who joined the San Jose staff in 2010. "Maybe this is what we need to get back on track. It's a big game anyway. We need three points and this is a showcase game."
Jahn said he was able to acquire 20 tickets for family and close friends and expects a lot more of his friends to be in the stands on Saturday. Last year's match at Stanford was sold out.
"I've heard it going to be packed," Jahn said. "It gets pretty loud up there, so I can only imagine how loud it gets on the field. It will add a variation to the game because we won't be able to communicate with each other as well. We'll have to trust each other to know what we're doing."
Jahn has practiced on the field in Stanford Stadium, which gave him some idea of playing in a bigger stadium. He got a second chance to work out, with the rest of the Earthquakes, at Stanford on Thursday, when San Jose held a scheduled practice there.
Wondolowski remains doubtful for Saturday night's game, so it may be up to Jahn to create some offense. It's a familiar situation for the two-time California Gatorade Player of the Year at Jesuit High in Sacramento. He was asked to carry a big load for the Cardinal.
He recorded 24 goals in his four years at Stanford, with 60 career points. He was a three-time all-conference pick and an All-West Region selection. Jahn came close to tying last week's game when he beat the United goalkeeper but bounced his shot off the post in the 73rd minute.
"He's a mature kid," Watson said of Jahn. "He's a fantastic person and professional. His passing has been good, he holds the ball well and he's been scoring goals."
Wondolowski also has made an impact on Jahn, who considers the 30-year-old veteran a mentor.
"He's very helpful," Jahn said. "He gives me advice directly on what runs to make and how to be calm in the box. Just watching him I can learn a lot. He has great movement and does well in the box. He's a great player and does so much for this team. If he can't play, it's up to us to our faith in our teammates and get the job done."
The Galaxy-Earthquakes rivalry dates to the first year of the MLS, in 1996. The two teams have matched up more than any other teams in the league. They've met 48 times in the regular season, faced off eight times in the postseason, and four times in the Lamar Hunt US Open Cup. The teams squared off in the playoffs in 1996, 2003 and 2005, as well as the 2001 MLS Cup.
"It's the history," Watson said. "There's the geographical proximity, but the games have been interesting every year, to the first year of the league."
Galaxy defender Todd Dunivant, also a Stanford grad, was San Jose's first-round selection in the 2003 MLS SuperDraft and played 46 games for the Earthquakes from 2003-04, producing one goal and six assists.
Dunivant may not recognize Stanford Stadium, as he predates even the Jim Harbaugh era. His final game in a Cardinal uniform was the 2002 NCAA championship game, a 1-0 loss to UCLA. That's the last time Stanford has advanced beyond the round of 16.