Akram Afif scored his third goal of the tournament to secure victory for the host nation and defending champions at Al Bayt Stadium.

As host of the World Cup in 2022, Qatar exited the competition at the group stage after three straight losses, but now maximum points from its opening two games in the Asian Cup have ensured it advances as group winner.

Afif lifted a shot over Tajikstan goalkeeper Rustam Yatimov in the 17th minute and Tajikistan finished the game with 10 men after Amadoni Kamolov was sent off in the 81st.

The other Group A contest between China and Lebanon finished 0-0.

After back-to-back draws, China likely need at least a point against Qatar in their last game to have a chance of advancing.

Both China and Lebanon's hopes of reaching the round of 16 are in the balance. While China are second in Group A on two points, they have the daunting task of facing Qatar in their final game, knowing a loss could see them overtaken by Lebanon or Tajikistan.

"We know that we depend on ourselves and that is something that every team would like to be in that position before the last game," China coach Aleksandar Jankovic said. 

"No matter if we play against a host country, Qatar, with their World Cup experience, we still depend on ourselves and I always like to be in this kind of situation."

Hassan Maatouk and Hasan Srour hit the bar for Lebanon either side of half-time, while Wu Lei thought he had broken the deadlock for China in the 65th minute, only for his close-range shot to be hooked off the line at Al Thumama Stadium.

China was quarter-finalist in each of the last two Asian Cups.

Lebanon lost 3-0 to Qatar in its opening game and sits bottom of the group with one point, but could still advance.

"It is a very important point for us, especially after a tough defeat against Qatar," coach Miodrag Radulovic said.