The South Korean signed for Spurs on this day in 2015 from Bayer Leverkusen and continued to look in good shape ahead of the new campaign, with his side brushing aside their Championship opposition.
Own goals were Tottenham's second-top scorer behind Harry Kane following the Premier League's restart last season and their luck has carried over as Omar Richards skewed a clearance into his own net after just six minutes.
Alli, who was seen to be on the receiving end of some string criticism from Jose Mourinho in previews of Amazon's All or Nothing documentary this week, produced a moment of quality in the 21st minute as he lifted the ball over goalkeeper Rafael after Lucas Moura's through-ball.
Moura was involved in a brilliant third goal six minutes before the break as he fed Steven Bergwijn, who teed up Son to fire home.
Half-time brought plenty of changes and one of them, Lamela, made an instant impact as he lifted a free-kick over the wall and into the corner.
Reading got on the scoresheet in the final 15 minutes when Puscas powerfully converted a penalty, given for handball on the line by Cameron Carter-Vickers.