No one at Highbury will consider the job done, but Arsenal can travel to Spain for the return in 12 days' time with a narrow advantage after an impressive comeback last night.
Having fallen behind to a Robert Ayala away goal which may yet prove crucial just before the interval, Arsene Wenger's team responded with two goals in as many minutes from Thierry Henry and, spectacularly, from Ray Parlour. They must hope that Henry's failure to add a third when one on one with Santiago Canizares does not prove costly.
Arsenal can hardly have expected a flood of goals against a side who arrived boasting the strongest defence in La Liga and the Champions League. In their 12 previous European matches this season Valencia's back line had been breached only six times.
A marauding run by Patrick Vieira set the tone Wenger had wanted as Arsenal began brightly and energetically, closing down quickly, snapping into tackles and showing a willingness to run at their opponents in an effort to knock Valencia out of their stride.
Freddie Ljungberg, in particular, saw plenty of the ball on the left flank, where it seemed Wenger had identified the 35year-old French full-back Jocelyn Angloma as a weak link.
More than once Ljungberg, especially eye-catching with the front of his hair dyed pink, skated past his marker and Henry also drifted wide to test his compatriot for pace as Arsenal seized the initiative.
Indeed, it was from a corner conceded by Angloma after an Henry run that Arsenal could, and probably should, have taken a 14th-minute lead. Robert Pires's inswinger fell to Vieira little more than a yard out at the far post, but the tall midfielder somehow directed his header against the bar.
Yet Valencia gradually settled and the counter-attacking quality of Hector Cuper's team was soon evident. Wenger had been able to call on his first-choice backline, yet they were stretched as Gaizka Mendieta, Kily Gonzalez and Juan Sanchez grew in influence. Arsenal had a lucky escape when Kily Gonzalez's deflected cross was knocked into the side netting by Sanchez, but the initiative had clearly switched to the visitors.
Arsenal were struggling to rediscover their early verve and it needed the outstretched leg of Seaman and a post to deny the gangling John Carew before Valencia took the lead from a fine move just before half-time. Kily Gonzalez began it, flicking the ball across the field to Mendieta and when the captain's cross was headed down by Sanchez, the Argentine defender Ayala volleyed powerfully past Seaman from 12 yards.
The Arsenal players reemerged after the interval in time to see the tail-end of a bigscreen tribute to David Rocastle. If that did not offer inspiration enough, Wenger must have hoped his half-time introduction of Sylvain Wiltord for Ljungberg would do the trick.
Wiltord lined up on the right side of a front three as Wenger sought to up the tempo again and regain the initiative. Straight away Valencia were on the back foot and although Arsenal initially looked unlikely to score, they suddenly burst into life with two goals in as many minutes to turn the tie on its head.
Henry got the first, finishing Pires's backheel after Kanu had miscontrolled a Wiltord cross, and the second from Parlour was spectacular, the England midfielder bursting towards the area and unleashing an unstoppable 25-yard shot into the top corner.
ARSENAL: Seaman, Dixon, Keown, Adams, Cole, Ljungberg (Wiltord 46), Vieira, Parlour, Pires, Henry, Kanu (Lauren 84). Subs Not Used: Manninger, Silvinho, Edu, Luzhny, Vivas. Booked: Pires. Goals: Henry 58, Parlour 60.
VALENCIA: Canizares, Angloma, Pellegrino, Ayala, Carboni, Kily Gonzalez, Mendieta (Vicente 89), Aimar (Angulo 68), Baraja, Carew, Sanchez. Subs Not Used: Palop, Djukic, Zahovic, Aurelio, Milla. Booked: Baraja, Ayala, Kily Gonzalez, Pellegrino. Goals: Ayala 41.
Referee: Dick Jol (Holland).
