Southee, who scored 14 off 19 balls after coming out to bat at No. 10, achieved the feat by hitting off-spinner Dhanajaya de Silva for a huge six during New Zealand's first innings on Day One of the ongoing Galle Test against Sri Lanka.
Both Tendulkar and Southee now have 69 sixes to their names in Test cricket. While Tendulkar took 329 innings to hit 69 sixes, Southee got there in just 89 innings.
The record for most sixes in Test cricket belongs to former Black Caps captain Brendon McCullum who smashed 107 sixes in 176 innings. He is followed by Gilchrist (100), Chris Gayle (98), Jacques Kallis (97) and Virender Sehwag (91).
On Friday, the Kiwis lost five wickets in the afternoon session, including the big wickets of captain Kane Williamson and Ross Taylor, as Sri Lanka deployed their three spinners throughout the extended session.
Left-arm spinner Lasith Embuldeniya struck a couple of massive blows in the second essay after failing to claim a wicket in the first innings.
Williamson charged down the pitch and attempted to hit one over the head of the bowler but didn't get the timing right and Kusal Perera at mid-on ran backwards for a terrific tumbling catch.
Akila Dananjaya then joined the party, when Tom Latham pushed forward with hard hands and ended up edging one to gully, where Lahiru Thirimanne took a sharp catch to dismiss the batsman for 45.
Henry Nicholls was dropped on 25 by Niroshan Dickwella off de Silva but couldn't capitalise on the opportunity after he was dismissed in De Silva's next over when caught by Kusal Mendis at second slip.