The Saints boss decided to use his £15million summer signing Dani Osvaldo as the lone frontman at Old Trafford instead of Lambert, who had to make do with a seat on the bench.
However, the 31-year-old England striker did come on in the second half and helped the South Coast side to the point their play warranted after Adam Lallana prodded home in the final minute.
"We have two very good strikers in Rickie Lambert and Osvaldo," said Pochettino.
"The thinking was to fill the middle of the pitch with more people that could keep possession of the ball.
"We also needed to be very quick on the flanks with Jay Rodriguez and Adam Lallana.
"The thing is the team has fully understood and knows how it wants to play. It has accepted how we want them to play.
"We pressure high up the pitch and that's been working out well for us.
"There will be some games that he starts and other games that he doesn't start, but overall he's a very important player for us."