Lewis Holtby opened the scoring with a close-range header for the Premier League side after 10 minutes but Gonzalo Pineda levelled from the penalty spot before the break following a foul by Michael Dawson.
Kyle Naughton suffered a head injury in a collision with Jalil Anibaba but managed to play on and see the first 45 minutes out.
Spurs boss Mauricio Pochettino made six changes at half-time before goalkeeper Brad Friedel was beaten by a thunderbolt from Osvaldo Alonso three minutes in as the visitors fell behind for the first time in the match.
It was not long before Tottenham were back level as second-half substitute Roberto Soldado slotted a penalty home after he was bundled down by Chad Marshall.
Former Spurs star Clint Dempsey, who made the switch to the Sounders last year, received a cheer from both sets of supporters as he was subbed off with 20 minutes to go for Sean Okoli, who set up Tristan Bowen minutes later as Seattle went in front again.
But almost immediately, DeAndre Yedlin was penalised for handball in the box and Iago Falque made no mistake with the resulting penalty to make it 3-3.
- Sports & Recreation
- Mauricio Pochettino
- Brad Friedel
- Lewis Holtby