David Wiese (2R) gestures towards Haris Rauf (2L) after the end of play at the Sheikh Zayed Cricket Stadium in Abu Dhabi on Tuesday night. AFP

Pakistan became the first team to reach the Twenty20 World Cup semi-finals after beating Namibia by 45 runs, with brilliant half centuries from Mohammad Rizwan and skipper Babar Azam in Abu Dhabi on Tuesday.

Rizwan finished with a slow-to-fast 50-ball 79 not out while Babar notched his 23rd Twenty20 international fifty with a 49-ball 70 to lift Pakistan — who won the toss and batted — to 189-2 in their 20 overs.

Namibia tried their best to match their opponents with David Wiese notching 43 not out and Craig Williams scoring 40 but Pakistani bowlers never allowed them a free hand as they managed 144-5 in 20 overs.

With four wins in as many games, Pakistan became the first side to reach the last four from Group 2. This will be their fifth semi-final in Twenty20 World Cup history — the most by any team.

Mohammad Rizwan (L) with Fakhar Zaman (C) run between the wickets. AFP

Williams knocked five boundaries and a six before he holed out to spinner Shadab Khan while Wiese smashed two sixes and three boundaries in his 31-ball knock. Opener Stephan Baard scored 29.

But Rizwan and Babar were the stars once again, like they were in Pakistan's win over arch-rivals India, which gave them a kick-start to the event.

The pair added 113 for the first wicket after Pakistan were slow out of the blocks, scoring just 59 in the first ten overs but ended with a flurry in the next ten, taking 130 runs.

David Wiese (C) greets Pakistan's cricketers after the end of play in Abu Dhabi. AFP

Veteran Mohammad Hafeez scored a brisk 16-ball 32 not out with five boundaries. Pakistan's total is the second-highest in this tournament, behind Afghanistan's 190-4 against Scotland in Sharjah.

Babar hit seven boundaries before he holed out to David Wiese in the 15th over while Fakhar Zaman was smartly caught by keeper Zane Green for five.

Rizwan reached his tenth half century with a pulled six off Wiese in the 19th over before hitting four boundaries and a six to take 22 off JJ Smit's final over.

Rizwan's knock included eight fours and four sixes.

Pakistan next face Scotland in their last match in Sharjah on Sunday. Namibia will meet New Zealand, also in Sharjah two days earlier.

Babar Azam (C) with Mohammad Rizwan run between the wickets during the T20 World Cup match in Abu Dhabi. AP

Pakistan went with an unchanged side for the fourth consecutive game after beating archrival India, New Zealand and Afghanistan in the Super 12 by successfully chasing.

Captain Babar Azam said at the toss he wanted to test his bowlers ahead of the knockout stage, but warned his team "not to get complacent” against Namibia, which defeated Scotland.

Babar Azam flips the coin at toss ahead of the T20 World Cup match in Abu Dhabi on Tuesday.

Namibia skipper Gerhard Erasmus was happy to bowl first on a pitch where seamers took nine wickets in the earlier game between South Africa and Bangladesh.

Stephan Baard was brought in by Namibia at the top order in place of Pikki Ya France while Bernard Scholtz made way for medium-pacer Ben Shikongo.

Lineups:

Pakistan: Babar Azam (captain), Mohammad Rizwan, Fakhar Zaman, Mohammad Hafeez, Shoaib Malik, Asif Ali, Shadab Khan, Imad Wasim, Hasan Ali, Shaheen Afridi, Haris Rauf.

Namibia: Stephan Baard, Craig Williams, Michael van Lingen, Jan Nicol Loftie-Eaton, Gerhard Erasmus (captain), Zane Green, David Wiese, JJ Smit, Jan Frylinck, Ruben Trumpelmann, Ben Shikongo.